umount: /home/diret/mount: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
I tried everything (fusermount -u) to unmount it but the only thing that worked was actually doing this:
ps aux|grep sshfs
Then I identified the sshfs connection and did:
kill -kill pid
After that it was obviously unmounted. I think it happened because the target SSH host crashed at some point.