There is something else, which seems totally unrelated, but somehow close: I see these past few days a big number of unread messages on some topics I am following (watching). These blue circles are on topics I am indeed following, not like the bug described above.
The number of “unread posts” is far higher than the number of actual messages in the topic. I suspect there was maybe this number of messages DELETED in the topic !? And the deleted messages appear as “unread” when they aren’t in fact there anymore ? Latest occurrence for me was this topic: Discourse Signatures (I am shown 92 unread messages when there are 4 replies in it)
This would be another bug related to “blue circles”/“unread messages”, I guess.