I read the first two threads in my image, but when I swiped back from this thread they show as unread and if I reopen them they load with the unread messages rather than the entire thread
Yes very few browsers automatically refresh a page when you back-arrow or back swipe. IE actually does do that, although I never use IE for other issues. I remember a while back attempting to code the index pages for an automatic refresh on back-arrow, however I seem to remember it causing more issues that it is worth. A refresh will update the Wash-Rinse-Spin indicators to what they are currently set at.
MattL you are correct that if someone embeds an image in a thread and it's not using https, the browser will complain about the content being mixed between https and http content. The image you embedded is causing this thread to do that. Not a big deal as far as I know, but time will tell.