Actually, AlfaODB plus the genuine MX adapter might be able to connect directly to the heated seat/comfort module. I believe some of the data points available in there are the seat pad(s) current, seat pad(s) temp and 1 or 2 others.
Based on the values for those data points, we should be able to determine with very little (or even NO) doubt why the heated seats are shutting off.
If the dealer claims they are shutting off on high temp, we'll see it. High current? Same deal. Can see the status of the switches too...maybe the switch itself is shutting down for some reason. Who knows. This is all stuff that Im not really sure the dealer ever tried to look at. As far as Im concerned, unless Im physically next to them, anything a dealer tells me they did for "troubleshooting" is suspect.
Further...since this issue seems limited to 2018, and the only "real" change in the 2018 MY was the head unit (where the heated seats have secondary controls built into)....could it be the programming of the head unit is glitchy and turning the seats off itself?