@hagak - Have you had any luck sorting this out yet? I'm running into the same issue with a new input expander I just added and can't seem to get it resolved. I get about 4 or 5 system restarts specifying the new M1XIN each day at random times, though it doesn't seem to impact the associated zones or arm status.
I just recently added coverage to my new detached garage on an Elk that's been running without issues for 5 years. I used the second allowable home run of the bus and ran 23awg cat 6 about 150ft to the new building. The remote building has an M1DBH with an M1XIN, M1XOVR, and a keypad and the latter two devices don't seem to have any (reported/noticeable) issues. I have an aux altronix supply out there and tied the negative back to the power supplies in the house. Power to the remote modules is good at 13.6V. Bus resistance measures at 65 ohms. I do get a fair amount of bus retry errors, though I always have on the first branch of the bus.. maybe 100 per day randomly across any/all of the other bus devices. The second branch doesn't seem to have added a meaningful increase in retries, though I have seen the new modules report such on occasion. The original/first branch of the bus has 4 keypads, 2 M1XINs, 1 M1XOVR, and an M1XRFTW. No issues with system restarts on the other M1XINs, though neither of these are powered from aux supplies either.
I did notice what you mentioned earlier in this thread as well--in RP, when observing the zone statuses in Area 2 (the garage), the voltage changes quickly and the state seems to lag behind a bit--maybe a minute. This doesn't seem to be an observable issue in the field though; for example, the door chime on the garage happens nearly instantly when the door is opened.
I've replaced and re-terminated all of the associated cables on the second branch of the bus with no effect. Hoping you may have figured something out in the last 6 months, or possibly replaced the board and resolved this. Let me know. Thanks!