I have a platform with Ethernet and WiFi and I usually use Connman
I have recently upgraded to Connman 1.38.
By our side, we have integrated ConnMan
on devices with a similar setup.
When preferred technology service is back, it does not go to Online
as it was doing with Connman 1.36.
I have provided several fixes / changes related
to the online state,
after the 1.38, maybe you can check them and try to test
with the master on HEAD, hoping it will solve your problem.