If in a public channel, someone with a nickname like "a^" writes something, clicking on the nickname to open a query, will actually open a query to a nickname that includes some HEX escape sequence instead, which won't work. Manually typing "/query a^" or double clicking in the list of users of the channel will work.
This has been fixed in https://invent.kde.org/network/konversation/-/commit/e55516e9fbc4d4ab3b7647219b66a0fe6da28940 which will be released with version 21.04