Additionally, I am using it mainly to sync folder with syncthing content.
The existing Folders are running smoothly. However, I created a new one a few days ago and started using it. After some time it disappeard like someone deleted it. Same behaviour after a restart.
The stock folder Android, Movies, Music and Pictures are not affected and remain and are in use.
Do write operations to the existing folders still work?
Newly written files/folders disappearing to me sound like the SD card is close to breaking completely. Had that a couple of times over the years and that is the way it begins. If that’s the case, only a fresh card will help.
thank you for your suggestion. Of course, I didn’t see the obvious solution; instead, I immediately thought of complicated ones… I checked the MicroSD in my Computer and I even wasn’t able to format it. I ordered a new one now.