Hi, I have an Ubuntu phone and it use syncevolution as backend for the contacts. I use command lines to have my CardDav contacts on my phone. But since I switched from self signed certificate to letsencrypt (related or not), I have tons of errors.

$ syncevolution owncloud contacts
[WARNING] owncloud: ignoring username , it is not needed
[INFO] @default/9frfrenchholiday: inactive
[INFO] @default/9rd2q8ps5e2r48skvidunfkoms8: inactive
[INFO] @default/addressbook: inactive
[INFO] @default/calendar: inactive
[INFO] @default/memo: inactive
[INFO] @default/todo: inactive
[WARNING] owncloud: ignoring username , it is not needed
[INFO @owncloud] target side of local sync ready
[INFO @owncloud] @owncloud/addressbook: inactive
[INFO @owncloud] @owncloud/calendar: inactive
[INFO @owncloud] @owncloud/memo: inactive
[INFO @owncloud] @owncloud/todo: inactive
[INFO @owncloud] @owncloud/contacts: using configured database=https://cloud.influence-pc.fr/remote.php/carddav/addressbooks/Vincent/contacts
[INFO @owncloud] @owncloud/contacts: starting slow sync, two-way (peer is server)
[INFO @owncloud] @owncloud/contacts: slow sync done unsuccessfully
[ERROR @owncloud] @owncloud/contacts: local, status 20048
[ERROR @owncloud] error code from Synthesis engine local, status 20048

Synchronization failed, see /home/phablet/.cache/syncevolution/target_+config@owncloud-2017-04-19-10-34-a/syncevolution-log.html for details.

Changes applied during synchronization (@owncloud):
+---------------|-----------------------|-----------------------|-CON-+
|               |       @owncloud       |       @default        | FLI |
|        Source | NEW | MOD | DEL | ERR | NEW | MOD | DEL | ERR | CTS |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|      contacts |  0  |  0  |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
|      slow, 0 KB sent by client, 0 KB received                       |
|      unexpected slow sync (local, status 22000)                     |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|          start Wed Apr 19 10:34:14 2017, duration 0:01min           |
|             unexpected slow sync (local, status 22000)              |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
First ERROR encountered: local, status 20048

Doing a slow synchronization may lead to duplicated items or
lost data when the server merges items incorrectly. Choosing
a different synchronization mode may be the better alternative.
Restart synchronization of affected source(s) with one of the
following sync modes to recover from this problem:
    slow, refresh-from-server, refresh-from-client

Analyzing the current state:
    syncevolution --status target-config@owncloud contacts

Running with one of the three modes:
    syncevolution --sync [slow|refresh-from-remote|refresh-from-local] target-config@owncloud contacts
[ERROR] error code from SyncEvolution unexpected slow sync (local, status 22000): failure on target side @owncloud of local sync
[INFO] @default/contacts: inactive
[ERROR] @default/contacts: aborted on behalf of user (local, status 20017)
[INFO] creating complete data backup after sync (enabled with dumpData and needed for printChanges)

Synchronization failed, see /home/phablet/.cache/syncevolution/owncloud-2017-04-19-10-34/syncevolution-log.html for details.

Changes applied during synchronization:
+---------------|-----------------------|-----------------------|-CON-+
|               |       @default        |       @owncloud       | FLI |
|        Source | NEW | MOD | DEL | ERR | NEW | MOD | DEL | ERR | CTS |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|      contacts |  0  |  0  |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
|      unexpected slow sync (local, status 22000)                     |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|          start Wed Apr 19 10:34:13 2017, duration 0:02min           |
|             unexpected slow sync (local, status 22000)              |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
First ERROR encountered: local, status 20048

Doing a slow synchronization may lead to duplicated items or
lost data when the server merges items incorrectly. Choosing
a different synchronization mode may be the better alternative.

So I decided to try some things I don't remember exactly (like forcing sync with refresh from local/remote) and changed the end of previous log by:

First ERROR encountered: local, status 20048

Doing a slow synchronization may lead to duplicated items or
lost data when the server merges items incorrectly. Choosing
a different synchronization mode may be the better alternative.
Restart synchronization of affected source(s) with one of the
following sync modes to recover from this problem:
    slow, refresh-from-server, refresh-from-client

Analyzing the current state:
    syncevolution --status owncloud contacts

Running with one of the three modes:
    syncevolution --sync [slow|refresh-from-remote|refresh-from-local] owncloud contacts

Then:

Data modified @default during synchronization:
*** @default/calendar ***
Comparison was impossible.

Since this step, I'm not able anymore to delete contact from my phone and make it sync on the server (to delete the contact on the server itself), instead the contact is just "cleared" (any information disappear but the contact is still here and keep firstname and lastname). I can sync contact created on the server on my phone and send contacts created on my phone on the server.

It seems the backup database is corrupted but I'm not able to reset completely my config. I just wanted to start by zero but I can't find any way to do this. :'(

phablet@ubuntu-phablet:~$ syncevolution --print-sessions owncloud
/home/phablet/.cache/syncevolution/owncloud-2017-04-20-11-04-b
+---------------|-----------------------|-----------------------|-CON-+
|               |         LOCAL         |        REMOTE         | FLI |
|        Source | NEW | MOD | DEL | ERR | NEW | MOD | DEL | ERR | CTS |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|      contacts |  0  |  0  |  0  |  0  |  1  |  0  |  0  |  0  |  0  |
|      two-way, 0 KB sent by client, 0 KB received                    |
|      item(s) in database backup: 2 before sync, 2 after it          |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|          start Thu Apr 20 11:04:51 2017, duration 0:05min           |
|               synchronization completed successfully                |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+

/home/phablet/.cache/syncevolution/owncloud-2017-04-20-11-05
+---------------|-----------------------|-----------------------|-CON-+
|               |         LOCAL         |        REMOTE         | FLI |
|        Source | NEW | MOD | DEL | ERR | NEW | MOD | DEL | ERR | CTS |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|      contacts |  0  |  0  |  0  |  0  |  0  |  1  |  0  |  0  |  0  |
|      two-way, 0 KB sent by client, 0 KB received                    |
|      item(s) in database backup: 2 before sync, 2 after it          |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|          start Thu Apr 20 11:05:24 2017, duration 0:05min           |
|               synchronization completed successfully                |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
phablet@ubuntu-phablet:~$ syncevolution --restore /home/phablet/.cache/syncevolution/owncloud-2017-04-20-11-05 --before owncloud contacts
[INFO] 9frfrenchholiday: inactive
[INFO] 9rd2q8ps5e2r48skvidunfkoms8: inactive
[INFO] addressbook: inactive
[INFO] calendar: inactive
[INFO] memo: inactive
[INFO] todo: inactive
[INFO] contacts: restore from backup
Data changes to be applied locally during restore:
*** contacts ***
Comparison was impossible.

[INFO] contacts: started
[INFO] contacts: restore done successfully
[INFO] Item changes that were applied locally during restore:
[INFO] +---------------------------------------|-----------------------------+
[INFO] |                                       |            LOCAL            |
[INFO] |                                Source | NEW | MOD | DEL | ERR |TOTAL|
[INFO] +---------------------------------------+-----+-----+-----+-----+-----+
[INFO] |                              contacts |  0  |  0  |  0  |  0  |  2  |
[INFO] +---------------------------------------+-----+-----+-----+-----+-----+
[INFO] The same incremental changes will be applied to the server during the next sync.
[INFO] Use -sync refresh-from-client to replace the complete data on the server.
phablet@ubuntu-phablet:~$ syncevolution --sync=refresh-from-client owncloud contacts
[WARNING] owncloud: ignoring username , it is not needed
[INFO] @default/9frfrenchholiday: inactive
[INFO] @default/9rd2q8ps5e2r48skvidunfkoms8: inactive
[INFO] @default/addressbook: inactive
[INFO] @default/calendar: inactive
[INFO] @default/memo: inactive
[INFO] @default/todo: inactive
[WARNING] owncloud: ignoring username , it is not needed
[INFO @owncloud] target side of local sync ready
[INFO @owncloud] @owncloud/addressbook: inactive
[INFO @owncloud] @owncloud/calendar: inactive
[INFO @owncloud] @owncloud/memo: inactive
[INFO @owncloud] @owncloud/todo: inactive
[INFO @owncloud] @owncloud/contacts: using configured database=https://cloud.influence-pc.fr/remote.php/carddav/addressbooks/Vincent/contacts
[INFO @owncloud] @owncloud/contacts: starting first time sync from client (peer is server)
[INFO @owncloud] @owncloud/contacts: sent 2/2
[INFO] @default/contacts: starting slow sync from client (peer is client)
[INFO] creating complete data backup of datastore contacts before sync (enabled with dumpData and needed for printChanges)
@default data changes to be applied during synchronization:
*** @default/contacts ***
Comparison was impossible.

[INFO] @default/contacts: deleting "test estse"
[INFO] @default/contacts: deleting "Gvv"
[INFO] @default/contacts: deleting 2/2
[INFO] @default/contacts: started
[INFO] @default/contacts: adding "test estse"
[INFO] @default/contacts: adding "Gvv"
[INFO] @default/contacts: received 2
[INFO @owncloud] @owncloud/contacts: started
[INFO] @default/contacts: slow sync done successfully
[INFO @owncloud] @owncloud/contacts: first time sync done successfully

Synchronization successful.

Changes applied during synchronization (@owncloud):
+---------------|-----------------------|-----------------------|-CON-+
|               |       @owncloud       |       @default        | FLI |
|        Source | NEW | MOD | DEL | ERR | NEW | MOD | DEL | ERR | CTS |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|      contacts |  0  |  0  |  0  |  0  |  2  |  0  |  0  |  0  |  0  |
|      refresh-from-local, 0 KB sent by client, 0 KB received         |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|          start Thu Apr 20 11:24:17 2017, duration 0:04min           |
|               synchronization completed successfully                |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
[INFO] creating complete data backup after sync (enabled with dumpData and needed for printChanges)

Synchronization successful.

Changes applied during synchronization:
+---------------|-----------------------|-----------------------|-CON-+
|               |       @default        |       @owncloud       | FLI |
|        Source | NEW | MOD | DEL | ERR | NEW | MOD | DEL | ERR | CTS |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|      contacts |  2  |  0  |  2  |  0  |  0  |  0  |  0  |  0  |  0  |
|      refresh-from-remote, 0 KB sent by client, 0 KB received        |
|      item(s) in database backup: 2 before sync, 2 after it          |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
|          start Thu Apr 20 11:24:17 2017, duration 0:04min           |
|               synchronization completed successfully                |
+---------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+

Data modified @default during synchronization:
*** @default/contacts ***
Comparison was impossible.