Very slow even on short replies

Very slow, even when just opened. CPU goes to 100% for 26 seconds for every reply. The reply themselves are shown very slowly (one word shows, then stops, then a few more, then stops, etc.). Profiling in devtools shows 98% of the time is spent in recomputeConversationTurnsForCurrentLeafId. I opened in incognito (so no extensions are running) and it is still slow. I’m using an up-to-date Chrome on Ubuntu.