It’s a glitch.
Someone mentioned to go to your preferences and set the number of threads and posts showing to 20 (usually it’s set to 50), and that fixes it.
I have the same frustration as you and followed the above suggestion and now I am able to see things “normally”.
That said, it would still be nice if this glitch would get fixed permanently — it does seem to recur periodically.
It doesn't fix it it just makes it somewhat tolerable.