I get a key error when I go to "sftp://192.168.1.155" but it works fine when I go to "fish://192.168.1.155". 
ssh to 192.168.1.155 does not complain.
The error dolphin shows: 
--
The host key for this server was not found, but another type of key exists.
An attacker might change the default server key to confuse your client into thinking the key does not exist.
Please contact your system administrator.
--

Its strange that fish works but sftp doesnt and the error message does not help.

Reproducible: Always