Username selection dropdown in chat freezes intermittently

Benjamin, the Avid Reader @loverofbooks (fc6bd8d5-94a2-462b-ac7f-9b03bc446d45): "Hey, I've been having frequent problems with the mention autocompletion on the website. I start typing someone's username and the autocomplete dropdown freezes. Once it's frozen, the return key and the up and down arrows don't work and the navigation won't go away.

There are errors in the developer console, they're just so vague that I can't figure out which ones are relevant."

I triggered this myself, and I'm not entirely sure how -- possibly because I typed most of the username myself? I think that's what I did. I grabbed the console errors at the time, though I hadn't cleared it first so there may be irrelevant errors. Pastebin of the errors: https://pastebin.com/LMmU2pLB