The 12V battery can be the cause of several issues. About a weeks ago, my backup camera froze then went black. I recalled just before it happened, I was using the infotainment for Apple CarPlay for video streaming for about an hour while charging the main battery, which could have lowered the 12V battery. However, after keeping the car idle for about 15 mins to recharge the 12V battery, the problem went away.
It seems to me that the 12V battery is not being charged if the vehicle is off while charging the main battery. If you happen to use the infortainment or anything that may lower the 12V battery, you may see some warnings/issues that may go away after some idle time to recharge the 12V.