Ah. You had changed the user in the /etc/default/plexmediaserver
file. That’s usually not used on modern Linux distributions (e.g. the official RPi distribution Raspbian). I had contact with plexpi before and was not very happy with how they handle things. So, I do not know if your user setting had really changed the PMS user to pi
or not. Most tutorials describe a completely wrong approach.
I can only recommend to use the official RPi distribution Raspbian (Debian) or Ubuntu. We can not support all those other pre-made images with prepared scripts and so on that do partially very stupid things. I am afraid, if you use plexpi and there is some problem, the plexpi community is your best hope of support.
FYI: Here is the official way to set the PMS user when you use the new PMS package or my old installer Linux Tips