I found the solution, after I’ve found the database error in the log.
I’ve had the same error as @tomservo over at:
I also had the missing seafile database table GCID and I also use seafile since version 6 I guess? Very strange, that we both had the same missing table.
(First I did backups, I mention this, just in case.)
So I entered the Docker container and stopped Seafile:
docker exec -it seafile bash
cd /opt/seafile/seafile-server-latest
./seahub.sh stop
./seafile.sh stop
Then I exited the container and imported the original database schema (copy it out of the container beforehand) into the mariadb database container:
docker exec -i seafile-mysql mysql -u root -pXXX -D seafile_db < /opt/stacks/seafile/data/seafile.sql
I then entered the container once more to start seafile manually.
docker exec -it seafile bash
cd /opt/seafile/seafile-server-latest
./seafile.sh start
./seahub.sh start
Afterwards I opened the WebGUI and tried a small upload: It worked immediatly!
Finally I opened the iOS app and uploaded a photo: It worked immediatly!
In the end, I thought it could not harm, to do some maintenance, now that I have a proper setup:
./seaf-fsck.sh --repair
./seaf-gc.sh --dry-run -t 3
./seaf-gc.sh -t 3
./seaf-gc.sh --rm-fs -t 3