One of my coworkers came across this oldie but goodie.
Their My Tasks screen was on the board view and they were organizing their tasks by urgency and it was deleting their due dates. I did a google and found this thread
which references the exact issues.
Removing the sort by due date fixes the issue but it’s so easy to accidentally do. The worst part is that it doesn’t record the due date change in the task log so you can’t easily put it back to the correct due date.