Acrobat X: comments won't show in sidebar list, even though they are there

[Jonathan_Dore]

I've just received a book proof PDF with 302 comments, but only 1 (a drawing markup) shows in the sidebar list. The others can be seen by their highlighting in the text, and the comment pops up when hovering, but they won't appear in the list. I tried importing the data file into a blank version of the same document, and the 302 comments suddenly appear there. However, when I save *that* version, close it, and re-open it, the same behaviour occurs. When I scrolled through the document page by page, the comments then began appearing in the sidebar as I scrolled past each page they were on  --  when I had scrolled to the end, all 302 were in the list. But closing and opening the file again, they disappear and this time won't re-populate the sidebar. The original file was very large (145MB), so I saved it as a reduced-size PDF (18MB) in case it was a RAM problem, but the behaviour is unchanged. In all other files with comments they are still appearing normally. Any thoughts?

[JR Boulay]

Can you share (part of) this file?

[Jonathan_Dore]

Thanks very much for your help. I'm attaching the first 50 pages here. There are 57 comments in this section.

[JR Boulay]

I guess there is a serious issue with this document.

See capture, at first the comments are invisible in the panel and then appear as I scroll through the pages containing comments.

I've never seen that !

[try67]

I did. It happens when the comments are created on a non-conforming application, usually on a mobile device.
One thing you can try is to export the comments to an external FDF file (after scrolling up and down, to make sure they are all visible), then go back to the original version of the file (before it got corrupted) and import them back into it. That might solve this issue.

[Jonathan_Dore]

Many thanks try67. I tried that at your suggestion but sadly the behaviour is no different from importing the comments directly from the PDF (i.e. they appear at first when imported, but if the PDF is then saved, closed and re-opened they've gone again). But it sounds at least as if you've identified the origin of the problem, which is a help  --  thanks very much.

[Jonathan_Dore · Accepted solution]

For the benefit of future users who might come across this thread, I confirmed with the person who marked up the file that she had done so in Microsoft Edge (though on a desktop machine, not a mobile device). So try67's diagnosis was correct. Unfortunately I am no nearer a fix for the problem.