This has been happening non-stop for the update a few days ago on my Dec 2017 MX.
Happens anytime the vehicle is stopped and the seat belt is released (in my case, driver seatbelt)
I've tried all sorts of workarounds, but it appears there is none.
I've tried:
Digging through all the menus on the console to see if there's some new 'Joe--' mode or something enabled or CYA setting to 'Disable annoying seat belt removal alert when exiting the vehicle'. Unfortunately, didn't find anything.
Waiting 30 seconds after normal park mode. Annoying seatbelt warning chimes when removed.
Putting it in 'PARK' by holding the button on the end of the stick until the emergency brake is engaged. Still annoying seatbelt warning chimes when removed.
Yeah, this is a trivial, but highly annoying bug, but I'm still not sure how it got past QA.
I've had to add a workaround to my routine to wait until the annoying chimes end when I get home late at night in order to not annoy my neighbors by opening the door while it's still going off (besides pausing or muting music - which I completely understand the reason I need to manually do it, but at least that doesn't make me cringe like the unwelcome seatbelt alert when exiting the vehicle)
Now that I realize it's not just my vehicle, I guess I'll be logging a bug report in the vehicle after it happens tonight when I get home.