Okay, I was reading along with a total of 37 message around 1030am on Tuesday, and after editing one of my messages had a glitch and suddenly there were no messages shown, just the top and bottom headers, but it still showed "reading 37 messages" at top.  I clicked my back button and I returned to my edit screen.  I clicked cancel and was returned to the empty screen again but this time it showed only "reading 12 messages," which was about how many I had left, probably.  So I went to the discussion home page to be able to see messages again and was able to read the last twelve. 

Of course the ability to set back an HMN is no gone since  we no longer have HMNs.  I believe I probably saw all the messages I hadn't read, so no harm no foul, just wanted you to know about the glitchy-seeming experience.