I have the same problem as everyone else. My bar is blank all of a sudden and before it went blank I couldn't complete the ask the spirits about ambrosia task.. Maybe it's because I already had a pac...
Ideas
So I went to the answers HQ link and tried the fix listed there. It worked. I was able to complete the whole week. It basically started me from square one (although I still had credit for the rewards I had already unlocked) and I had to do the event again, but it went so much faster the second time because I had already unlocked the grimaphone. I did not expedite the mail service, just waited until it showed up naturally. I was able to use the seance table, plant the flowers, read the newsletter, do everything normally. I even was able to keep my custom content (not mods, nothing that affected actual gameplay or UI. just cute clothes and hairs). I did have to purchase the skill books you get through the event (because I had unlocked those in a different save and it didn't transfer) but they aren't that expensive, so I didn't mind it, also you can complete the event without them, it just takes slightly longer.
You can find the fix here