M1ABD-3 stopped working overnight last night. I visited the site this evening and found that just a re-boot of the computer and TNC is all that was needed.
The problem seems to be with the very old Timewave PK-12 TNC that we use. It seems to get confused and stops working every now and then. It just needs to be switched off and back on while the computer is not connected to it.
M1ABD-3 is now back on the air again.