Connection error when user credentials are correct

I had a rather odd problem with a connection today.
It worked fine previously but here is a list of things I've tried and what happened:

- Connect with correct credentials and host in format IP:port /admin with rdp, not using RDM: connects without issue.

- Connect with correct credentials through RDM: Gives the can't reach remote computer error.

- Connect with wrong credentials through RDM: Shows the incorrect credentials prompt. Signing in with correct credentials here gives the same error as above.

- Checking the Restricted admin checkbox under the Advanced tab then connecting with correct credentials through RDM: Connects but gives following error message in the session "Account restrictions are preventing this user from signing in. For example: blank passwords aren't allowed, sign-in times are limited, or a policy restriction has been enforced.".

Could it be because of the /admin part? RDM auto removes it and the port from the host field but as far as I can see only the port info is inserted elsewhere.
I am rather new to RDM and remote desktop in general, so what is mentioned above is the full extent of my troubleshooting, except for refreshing RDM between changes.

Thanks in advance