I’ve been seeing this issue on Firefox too. An interesting follow-on is that after seeing this error the display of messages on the thread often chokes as well - if I scroll down from the point where I was trying to expand replies, it will just stop at some arbitrary point as though that’s the end of the thread even though I know there’s still more to see.
I’ve been seeing the same results from expanding from the reply (to see the messages it was a reply to) also.
