To stop spamming Seafile drive client is ready for Ubuntu and Debian I try to log my findings here instead:
So the problem really comes from the fact that we have our home directories mounted via NFS with Kerberos.
This leads to the behaviour, that processes executed with sudo or ones with the setuid bit (like fusermount) can not access the home directories because they don’t have access to the Kerberos ticket.
After reading https://bugs.chromium.org/p/chromium/issues/detail?id=508744, I tried to change permissions on the fusermount binary (removing setuid and adding the capabilities) and voila, I can stop and restart SeaDrive.
Now my preferred solution within the SeaDrive client would be the possiblity to change the location of the SeaDrive and .seadrive in the setup wizard and the config file.
Best wishes,
Moritz