For a few months now I have often seen the red dot on the review queues icon, which is meant to indicate that there are posts that have been flagged as low-quality in the queue to be reviewed. (For anyone wondering what I'm talking about, know that one must have review privileges to see the review queues icon at the top of the page.) The red dot often persists through a page refresh. When I click on the icon, there is a red dot in front of Low Quality Posts. When I do click on Low Quality Posts, I'm usually told that "This queue has been cleared!"
In other words, I often see a red dot on the review queues icon when there are no low-quality posts in the queue. This appears to be a bug.
Here are pictures from a very recent example. I took care to refresh the page immediately before I clicked on the review queues icon with the red dot.
"Oh look! One of the review queues needs my attention!"
"Aha! There are Low Quality Posts to review!"