For whatever reason (likely due to a change in the wiring, or just to the trickyness of the wiring to the front end) there were a couple of wiring mistakes in the h2susauxb478 model. I consulted H2 aLIGO BS, ITM and FM Suspensions Controls Wiring (D1001725) and was able to clean it up as best as I could. The model was then recompiled, installed, and restarted on h2susauxb478.
So it turns out that the wiring change was due to a reconfiguration of the cable layout to the QUAD M0 and R0 stages, as specified in #1508 and #1513. The wiring diagram in v7 of D1001725-v7 reflects the proper changes, and this is what the SUSAUX models were brought into line with, so all is good.