My dedicated server is in the recently played list, however, it is greyed out.
I then tried connecting via the invite code and was unsuccessful.
I restarted my server and it's running fine, but it's still greyed out in the list.
Using 1 mod on the server and client side's, 50 x fast travel points, haven't had any issues at all with it except for 2 player's that have no quests showing in their journal's though they can still see quest icons on the map and can complete them and gain xp with no issue.
I removed the mod to see if the server would show up without it, however, it's still greyed out and inaccessible, so doesn't seem to be mod related.
Co-op is also inaccessible - the only game mode that currently works is Solo.