I observed the missing task list bug and after deleting a bunch of files and running repair twice, I was able to see the tasks again. Progress on them had completely reset (previously, I had asked one person and read the letter) - but it was back.
Since I didn't have time to actually play through the event right now, I saved and quit after a bit, hoping to resume this evening.
But out of paranoia, I immediately reloaded my save - and the task list was missing again.
My current suspicion is that simply quitting the game without completing the full week's activity is enough to break it for people, and that the only ones for whom it is working are those who played through the quests in one go.
For completeness sake, the ~complete list of things that happened in my session between verifying that I could see the task list again and not being able to see it:
- My sim finished one of two homework assignments (in the kitchen).
- Her dad showed up at the front door again, and finally fed up with having to walk over and let him in every time, I gave him a key.
- They chatted for a bit before I sent her off to do her second homework assignment. She walked into the bedroom to work on this assignment.
- She was interrupted 2-3 times from finishing the homework, kept trying to getup and go talk to him in the kitchen.
- Eventually, I got her to just work on the assignment.
- After about an in-game hour, he walked into the bedroom to chat (I didn't expect the house key to allow that) - blocking her path to the door.
- As it was time for her to run off to class, I cancelled her homework and the conversation, but the two just stood staring at each other for a while - even after I told him to leave.
- Eventually, he walked off, but she just stood there glitched. So shift-reset her and she ran off to class with like 20 minutes left.
- Then I saved and quit to menu before re-entering the game without quitting sims completely.
So yeah, just a normal 10-15 minutes of gameplay that should not have interacted with the event quest in any way. It is possible that her getting glitched out was somehow related to the event dying or something... but I doubt it.