Bug reported by phant at IRC libera.chat:
16:20:21 <phant> and anyone who does /who on a channel you're in will be disconnected 16:20:36 <phant> some clients do that automatically, that's why i kept getting kicked before
Apparently, the way /WHO works began crashing clients.
After comparing output of /WHO in solanum (libera.chat) and IRCat:
I will change the two above and see if this fixes things.
This bug has been fixed in commit dbcd4b8755.