8debe99 created the issue
If in your ~/.ssh/config file you have an entry with the "Host" different from the Hostname entry the Hostname is not used.
e.g.
Host server
Hostname 192.168.0.100
IdentityFile ~/.ssh/my_key
Cyberduck attempts to connect to "server" rather than the machine defined by Hostname "192.168.0.100"
The following entry does work but is less user friendly
Host 192.168.0.100
Hostname 192.168.0.100
IdentityFile ~/.ssh/my_key
If in your ~/.ssh/config file you have an entry with the "Host" different from the Hostname entry the Hostname is not used.
e.g.
Cyberduck attempts to connect to "server" rather than the machine defined by Hostname "192.168.0.100"
The following entry does work but is less user friendly