Phone shuts down after a while

I’ve got a Teracube 2e (not that it matters). I let it fall quite often already.
Sometimes, once every few days, mostly when low on battery, the phone shuts down.
I don’t think it is when the phone is working hard, only when when I lock the screen, it does this.

I already switched batteries and it happened too.
What do you think the problem could be?

I could check if the battery contacts are not dirty…
Something wit low usage of battery?

It seems you have installed the Android 11 update yesterday. Could you observe a few days with the new update?

Oh no, it was even before the update.
I am trying to track the hardware resources and seeing on what battery percentage it shuts down.
The phone behaves normally, so I never expect it. But I do think it has something to do with the power delivery… I got a spare Teracube 2e for when it really becomes a problem.