Comments Not Showing on PDF

We send out manuscripts in PDF form to a proof reader, they mark up the pdf and comment within the pdf then send it back. We can see there are highlights/comments made, but the comments do not actually show up in the comments pane. I have researched hours on this, attempted to update my version, spent an hour and a half on chat/remote in on my computer with Adobe Support, nothing has come up with a solution. This has been happening for about a year now with no solution.