[Alan_SP]

Yes, this looks like something hard to replicate.

Probably you could try to register, but before actual successful email confirmation, try to "play" with test user, for example, surf site, maybe even go to link for manual email confirmation, or use invalid confirmation link...

Anyway, try to create these multiple threads without username. This happens, but what users actually do, I can't tell.

Problem also is, I could try to ask users (I have one user who probably triggered thread creation without name), but I'm not sure they would be able to describe meaningfully what they did. They usually not very tech savvy and they certainly didn't pay attention to what they are doing.

Also, if you find out what's actual users' behavior who trigger thread creation, I could try to explain to my users who have problems confirming email address what (not) to do. I have relatively lot of people who fail to confirm email address, but I think they just have problems with computers and internet in general, not that something is really wrong with my setup, as there are many (including myself) who manage to register without any problems.