I've seen this happen in the wild, again! Or at least, something that has apparently the same causes. It wasn't an ask sent to me, but one that a friend had linked to, where the asker's page had recently been set private.
New buggy interactions of note:
Simone
The short version is, I responded to an Ask I received, but then the post didn't show up on my timeline or profile. I was getting notification (numbers) on the post, but nothing was showing on the notifications page about it.
Oddly enough, I went to my own profile page while logged out and was able to see the post just fine.
Turns out, this likely was because the Asker set their page to private. I think the steps are as follows: