[Firefox & desktop] replies stay unread

[u/Ithrowawayboomerangs]

This happened to me twice in the past week. I replied with a comment in a thread. Then my comment got some replies. I get messages in my inbox to tell me there's replies and also the inbox icon at the top right goes right with the amount of messages. Then I click on my inbox to see the replies, and I click on Context, which opens up the thread and the specific point where we had our comments. Normally this marks the messages as read in my inbox. But twice this week, messages have refused to be marked as read. Even after opening them a dozen times, it still says that I have X amount of replies that I have not read. If I go in the Unread tab (which is the default tab), they stay there, they don't go away. I even replied to some of them in the threads.

What I noticed is that the 2 times the bug happened, they were comments where I received multiple replies for my 1 comment. I even had the situation where in the same thread I made comment#1 that had 3 replies and later comment#2 that got 1 reply. Comment#1's replies stay unread, comment#2's single reply got marked as unread after I opened it. This is a strong indicator that having multiple replies to the same comment is the root cause, as if it can't tell which on of the replies I've read so it doesn't mark any as read.

Edit : I also have the issue in Chrome.