OK, I finally have more data. I switched the TB-10 bases back in December, and both were stable for a week or two, but then the problem followed the base. About a week ago, a new failure mode occurred. The TB-10 just sat there and the lights blinked as follows: (1) Power on (2) Ready on (3) both off. This happened indefinitely until I wiggled things and whatever was intermittent was restored. It happened again today, and I was able to isolate the problem to the connector on the left side of the TB-10 (sockets) that ties it into the FieldPoint Bus. I have pushed the modules together numerous times, so I'm sure they are secure.
I'm assuming at this point that there is a problem with this connector, and I've applied ProGold, a lubricant/conditioner I've used before, to one of the malfunctioning systems. We'll see if this helps. I guess the next step will be bending the connector pins a little to try to make better contact. More updates soon.
James