Replaced RMYoung with a METEK, using the same port since all are filled. The arrow is pointing towards the tower in direction of boom. We discovered that the fuse to the serial interface boards would blow eventually once the METEK was running, so we replaced the 1A fuse with a 3A. The configurations have been updated and all appears to be working now. Port 1 is jumpered for RS485.
Replaced RMYoung with a METEK, using port 5, now jumpered for RS485.
No change.
We have added rsync monitoring to nagios, and discovered that a few sites are days behind on rsync. It turned out the problem was the Ubiquiti not allowing certain traffic, same symptoms as documented in ISFS-152. Two of the four systems were tnw05t and tnw05b, the same ones as reported in the original issue. The problem keeps happening within several hours after rebooting the Ubiquiti, so there must be something particularly wrong with the radio at that site.