I didn’t think rules were included in free plan, but maybe these My Tasks rules were an exception as you say you’ve had them working for years.
Am I correct in assuming these rules with the old rule builder? (Trigger to action in direction top to bottom as opposed to left to right)
I’d like to propose a workaround for this specific rule. You can group My Tasks by due date instead of sections. This means you won’t need to use rules anymore to group tasks by due date. You can find more info on group/sort/filter options in this thread: 🪄 Design magical tabs with group, sort, and filter!
Meanwhile flagging this thread for @Forum-team to see if they might know what’s going on.