I’m afraid the problem is in the iPhone. I have used the same power bank for years and then it suddenly started disconnecting and reconnecting by itself, alternatively. I thought it was a power bank issue and I bought a new one. Same problem.
As I am typing, I’m using the power bank. It works fine, but the issue reappears if I reach 33% of battery level in my iPhone. Exactly 33%, no matter what the phone is doing or which power bank I’m using.
My guess is that something has changed at software level that stops changing when the absorbed current is too low, or the voltage is too high…