Sucks that this has been your experience and admitted it does take a bit of work to set it up nicely.
The documentation of how artwork is detected and ways to fetch it automatically from online sources you can find here
The multiple profiles thing happens Because Navidrome is very tag dependent to understand music. I have a few collections where the band slightly evolved their name/spelling where this happened.
The difference between “artist/albumartist” and the “compilation” tag need to be set correctly and uniformly for that to be fixed, which depending on the source can take some work.
My own strategy is to start with a small server And gradually expand it. Make sure the tags are ok, the art is correctly named in the right spot.
I still have a lot of music i haven’t processed
For the music that did get processed, things are stable and reliable as rock, require no maintenance and performs very well.
The removed albums thing Is a weird one though, using the full rescan off all files and data button I have never experienced this.