Unreliable 4G LTE interface IP address

Hi, I am running 4G LTE managed by ofono version 1.30 and connman version 1.37, it works well most of the time, but occasionally, the 4G modem is connected, there is no IP address so I have to run systemctl restart connman to bring the IP address back. As it is intermittent and random, it is hard to debug, any insight advice what I could be missing, why couldn't connman pick up the 4G LTE IP reliably? Thank you. Kind regards, Jupiter