Hello,If you have a SSHFS entry in fstab, then it shouldn't be Dolphin handling the SFTP aspects? (Dolphin plugin should be involved only when using "remote places" or "sftp://"; in dolphin)
On my side, I had general SSH key/passwords issues few months ago, following a switch to sid. At some point it worked better disabling GSSAPIAuthentication (NFS/Kerberos in the loop)…
until I noticed I had wrong permissions set on my ~/ & ~/.ssh/ folders! Hope this helps, good luck. Vincent
