I also just updated to the most recent version – v126.96.36.199 to see if I was having the same issue, and it still exists.
Attached are the 3 test rules I’ve tried.
The 1st one, I am hiding all multichoice fields when nothing is chosen.
The 2nd and 3rd ones, I am showing the related multichoice fields.
When I choose a 3rd choice, the 2nd field is replaced with the 3rd. Could it be an “overlap” issue? I don’t have any side-by-side settings in place.