Why did the iPhone, after charging from a mobile battery, begin to incorrectly show the charge level as a percentage frozen at 95%?

Question

iPhone

I bought a Canyon CNS-TPBP10DG portable battery, fully charged it, and the next day I decided to charge my seventh iPhone from it. Everything went fine, but when the battery was charged to 96%, it stopped charging further, although the lightning icon continued to hang on the battery. I took the phone off the charger and used it as usual for 2 days.
Now I put it back on charge from the same battery and the battery level again hung at 95%. The charge seems to be still going on, but the numbers do not change. Disconnected from the bank, listened to music for half an hour, but the battery hung at 95%. I rebooted the phone, the percentages began to decrease, in the usual mode for them.
What is it? Powerbank fault, phone hardware or software bug? I used the original cable. When charging from a native power supply, such glitches have never been observed, so for the first time I encountered this. To be honest, I'm even a little afraid for the health of the battery in the phone.
Does anyone have any thoughts on this?

Answer 1

And when charging from a native bp, it reaches 100%?