Yes, I'm very sorry about this. We have a routine that fixes the bottleneck of users registering all at the same time (which has worked up until now), but this appears to have "broken". We hope to fix that very soon.
In the meantime, I'd suggest disabling the "dynamic registration" and "auto member on registration" settings. This will mean that new members won't show on your memberlist until they actually post. Hopefully you won't mind using this "workaround" for a little while, until we can fix the problem.