LMS Problem on PCp 8,0

Hello everybody,
i installed pcP 8.0 64 on Rpi4. Later i installed the LMS via the pcP routine.
As to the innformation on LMS Version 8.20 is installed. I mounted my external
USB HD /mnt/music. As to the "information" all my music has been found by LMS.
So here is the problem:
1. in the player-mask of LMS (Web interface) no album etc. is shown
2. when going to the point "plugins" nothing is shown
3. when restarting the LMS i have to chose the music source drive again as all other
settings have to be done again.
What did i do wrong?
Greetings
ulf