I’ve had a look on the forum here and didn’t find a similar issue, although I do see other rebooting / charging forum discussions.
I’m usually charging from either my laptop, or a built-in USB charging port on a mains socket.
Different cables, different amperage… same phone
The phone continues to charge - right up to 100% - but after each reboot the phone will (correctly) check for emails, etc and I’ll just have several musical notifications after each reboot… a bit annoying after a while.
I haven’t made any meticulous notes, but this appears to happen at lower charge levels (ie 40~70% range)…
By the way charging to 100% does push the battery to a limit, strangely the two figures you mention are an ideal range and not at all low, well 40% is getting there.
Heat whilst charging is an issue, hence not to charge to 100% over night, when you can’t disconnect it and keep below 90% charging when the environment.
Charging from the PC or the mains, with a USB A socket may be good for a slow charge, which will limit any over heating, but unless they have a QC protocol then the battery cannot communicate to lower the input. But if the outputs are only 5V then it should be fine.
You may have a loose connection in the phone, so you can check that.
There may also be dirty contacts which you could clean.
You can try using in safe mode to see if it a app conflict.
If you an SD card check it is formatted at Portable/External
Check how much memory you have left and clear app caches etc.
