Hi Thomas,
Assuming you tried restarting the nodes and the problem persists, have you checked to ensure external ports are open on your relays externally?
Are there any clues you can provide in your log files?
Also, on a side note, have you ever ran 1.18.1 on these nodes?
Please refence this thread as well - if all else fails you may want to try deleting the db directory and starting over: