The bug “seaf-fuse is already running, pid nnnnnnn #2887” on GitHub (I somehow cannot insert links here) seems to be fixed, Seafuse starts without issue.
However, I still cannot see the files on the host (although I can see them inside the docker container in /seafile-fuse).
Without Seafuse started, I created a file within the docker in /seafile-fuse, which I see on the host just fine, so the volume mapping seems to be working. But once I start Seafuse (after removing the file again since it needs an empty directory), the folder on the host is just empty.