My Nokia 7.1 started exhibiting funny behaviour today. It boots up on battery just fine. As long as I don't try to get past the lock screen, it happily stays on too.
But if I then unlock the screen without plugging it in, I just see "phone is starting" for a few seconds and then the phone shuts down.
If I plug in, the phone starts normally, but as soon as I unplug past the "phone is starting" point, it shuts down.