After the small upgrade from 9.0.9 community to 9.0.10, no avatars are shown, so is there any migration script needed? How can I fix the issue?
Try to clear /tmp/seahub_cache
I actually did, but it did not work 
also clearing the browser cache did not help.
Maybe, it is related to [Bug] Seafile crash after update into a Docker from 9.0.9 to 9.0.10
OK. Fixed it. I had put a symbolic link to the seahub-data directory (which is release-independent). This obviously did not work (also not in version 9.0.9), but in the old installation, the avatars directory was still filled. Conclusion is that the folder
/opt/seafile/seahub_data/avatars
should be used but maybe does not work with a symbolic link and
/opt/seafile/seafile-server-9.0.x/seahub/media/avatars
was used instead. I am not using docker, so I am a bit confused. I thought that it would be sufficient to let /opt/seafile/seafile-server-latest to the most recent installation directory while the avatars are accessed via /opt/seafile/seahub-data/avatars
The reason was simple: I am using an external reverse proxy, so I decided to not use an nginx instance on the same server. Consequently, the location for avatars is not redirected to the right directory:
location /media {
root /opt/seafile/seafile-server-latest/seahub;
}