This happened to me day before yesterday. I unchecked the "formatting in comments" option in the book details settings and got them back. That might work for you?
Now the comments only appear when that setting is unchecked. Not when it is checked. I don't know why. And I'm not sure what triggered it.
I posted about it here:
https://www.mobileread.com/forums/sh....php?p=3805752