Did you ever get this issue resolved. We have the same issue. It only started after the April upgrade on our 2021 Santa Fe.
Yes, normally the seat will move after 30 seconds or so by which time I have reversed out of the garage onto the road and I'm just setting off in drive but occasionally it's taken longer (or I've maneuvered quicker ) and I'm half way down the road and the seat starts to move back to my position while I'm travelling 25mph +. If you're wondering why I don't just push #2 on the door after switching profiles it's more out of frustration that it used to move immediately until the first upgrade and (as an engineer) I want to know when it will move. Once it didn't move at all before I reached my destination. Upon returning to the car the seat then moved from the engine off position (fully extended) to my position - that was an interesting data point.Driver seat unexpectedly moves while driving down the road?????
I would agree were it not for the fact that the issue first arose immediately after the first upgrade last November (or so) and now after the latest upgrade the issue is even worse - before the seat would always move within 30 seconds or so now it's random if it moves at all. OTOH the OP's reporting the a new main board plus a complete reset didn't address the issue supports your position that it's an environmental problem.Maybe they should utilize a TDR to trace 'grounds' on each of the suspect computers.
Both upgrades were via USB contains software downloaded from Hyundai’s website. While the upgrades were described as navigation upgrades they also changed the display screen layout and features e.g. sorting radio station presetsYou mentioned the 'upgrades'; were these downloaded nav updates or a platform-specific dealer install?
Sorry, j should have updated my post. It worked for us for 5 days or so - maybe 4 changes of driver. Then it stopped working when switching back to primary (wife) but still works for me.I performed the factory reset and then rebuilt my wife’s and my profile. It did indeed work twice! If I go back to the original suggestion and wait for the one screen prompt at start up times out, and then go to change user, it works every time. Apparently the pop up start up screen does not work properly to actually change the user. It was still a PIA to reload my FM and XM stations, and other setting again after the reset. I wont do it again until Hyundai fixes the issue.