I just had a few users tell me that they cannot see attachments on a thread. The user attached the image and then inserted the full image. I can see them myself, we use proxy image and SSL and it works fine to me on the URL and the thread but some are reporting that they cannot see it. Two of them were on a Mac and one was on an HP laptop with Windows.
A few other users who tested it can see them fine on various devices so I am not sure what the issue is. Registered usergroup has permission to view attachments and upload them and we have no additional image handler other than one which uploads to another site and does not interfere with the attachment system as I disabled it, tried it again and they can still not view them.
Note: They cannot see any images in that thread apparently.