The Cylc default is to use the full hostname here (i.e, the name of the box), but it could be that localhost is the name of the box, or that host self-identification is hardwired to localhost.
Either way, you’ve confirmed that this works with that cylc ping command, so I think we’re good here. Would expect all the commands which interact with workflows to work given this (you would need to observe the workflow log to determine this due to the Tui / GUI issues you’ve reported).
My guess is that there’s a long and a short form of your username
Here’s an idea which might help to confirm this if it is the case.
Can you check if the output of these commands agree with each other?
whoamibash -l -c 'whoami'bash -l -c 'echo $USER'python -c 'import getpass; print(getpass.getuser())'