As a first level of troubleshooting communication problems with the hardware watchdog chassis at EY, I replaced the EY chassis with a known good chassis from the DTS.  I then tested the (former EY) chassis in the DTS, it works properly.

Presently, hardware watchdog chassis S1301709 (formerly from DTS) is installed at EY, while hardware watchdog chassis S1301712 (formerly from EY) is installed in the DTS.

Given that the S1301712 chassis communicates well in the DTS, I don't expect that this solved the problem at EY.