Sorry for the inconvenience caused to you.
Kindly share with us your machine details and Acrobat version.
Also please provide us some sample files on which you are facing this issue
An error occurred while saving the commentBrian D. Miller commented
I have been having this issue for months - did not make the connection to computer going to sleep, but that matches with my operation. Our IT department has set a very short period of inactivity before the computer lock screen comes up. Without doing a tightly controlled test, I think that the document on-screen sometimes survives sleep mode and sometimes doesn't.
I use Acrobat Pro to add various comments, including lines and shapes to engineering drawings in PDF format. One fortunate thing I have found is that Acrobat usually lets me save a file (accurately so far) even if it cannot display it. If it can't, the comments frequently are still showing, so I (a) make a copy of the original PDF with a changed name, (b) open the copy in Pro, and (c) copy the comments to the document copy.
I'm using Acrobat Pro DC on Windows 10 Enterprise LTSC, on a computer with an Intel i5-8365U CPU, on-board Intel graphics, and 8 GB of RAM.