I'm using Adobe Acrobat Reader DC, Continuous Release version 2019.021.20061 (on a Mac, if that matters). I just downloaded it about a week ago.
I left about 90 comments in a PDF, and when I opened the document today, the comments are still there (as yellow boxes on the page and in the right sidebar), but the text has disappeared from about half of them. There are also some doubles of the same comment, but that's not a big deal. I'm wondering (1) is my work gone or is there a way to get it back, and (2) is there a way to stop this from happening again?