I encountered this issue yesterday (March 2025). An instructor noticed that many of his students were missing assignments since the beginning of the semester--even some of his best students. When he questioned them, they said that the items never appeared on their To Do lists or on their calendars. It seemed to be completely random, but the missing rate was quite high.
Because there is a similar issue with Students missing from SpeedGrader and imports, I checked a little further into the import. Section 01 was imported from the previous semester, the automatic date selection by the system was used to change all the assignments dates. Since it all looked correct, no changes were made. Then the 01 course was imported into section 02. The only thing that needed to be changed was the time on all assignments, which the instructor manually changed, then saved.
The interesting thing is that the To Do lists were working correctly in section 02 where there had been a slight change to the time, and then they were saved. But those same assignments were not working in section 01, until the instructor changed something and saved.
A quick search on Google of “Issues with To-Do lists in Canvas” displayed this:
Canvas "To Do" lists can display incomplete information or have issues with assignments not appearing or disappearing prematurely, especially when courses are copied and due dates aren't adjusted, or when assignments lack due dates. Students should also be aware that the mobile app's To Do list only displays upcoming course activities.
Course Copy Issues: When a course is copied from one semester to the next, due dates might not be updated, causing assignments to not appear on the To Do list or missing submit buttons.