Most titles gone, music there

I use Audirvana on my mac for years. Since two days I noticed a severe issue: Audirvana does not show any titles anymore. Not on the app on the phone, not on the Applicaton on my mac. The mac has the newest version, the audirvana app is on the newest release.
Not all titles are gone, some, from music I imported a day ago, are there. But all others are gone.
I use folder watching and nothing regarding itunes
Action 1: Resync. No help
Action 2: Check Database integrity and indexes: No help
Action 3: Remove database in library folder and reimport all music files: No help
Action 4: Remove everything on my mac regarding audirvana, install app from scratch, choose folder to synch wait for synch to finish: No help
On my remotes also no titles are shown anymore.
Now, Audirvana is useless for me.
Any help? I thought reinstalling everything and importing all tracks from scratch would help, but it doesnt.

It seems something happened to you db and reinstall is not the route as it will always use the db found from previous installation
I suggest you to restore the db from the latest backup you have before the date you started to face this issue

I removed all the database files in application support and started completely from scratch.

I installed it on a new computer which never saw audirvana. Now, most of the titles are present, but none of the artists. Although it shows me the artists sorted in the artist view, but each track has no artist. And I can also not select all tracks of an artist to add it manually. I would have to go album by album.
I spent so much time now figuring out what happens and nothing seems to help.

This means metadata are missing … it is correct not to be able to change them all together but per album
… but this seems strange to me, maybe it is just missing the artist column.
When you are in the track view right click on the row (blue) where you read Album, Title ecc… and select all the metadata you want to be displayed