Some of my documents do not show all the comments when opening. One specific document only shows 8 but there are over 80 comments. This is not computer specific because the document does the same on multiple different computers as well as different Adobe versions.
Hope you are doing well and sorry for the trouble. As described you are unable to see all the comments in the specific PDF file.
Make sure you have not filtered the comments in the comments list. For more information please go through the help page https://helpx.adobe.com/acrobat/using/comments.html and see if that works for you.
Also, please share the PDF file with us so that we can check it at our end. https://helpx.adobe.com/document-cloud/help/sharing-pdfs.html
This happens when the comments were created in a non-compliant PDF viewer, which results in corrupt comments.
If you scroll down the pages they would probably appear in the list. I bet you won't be able to edit them, either.
Can you share an example PDF?
While it is possible that the comments are added in a non-compliant manner, one needs to analyze the PDF to be sure.
And what makes you sure that the document indeed has more comments than you see?