Don't you think it is slightly irresponsible that you upgraded to an unsupported version of the software, that is in its first beta, despite many warnings that you should only do so on a dev/test environment and even then only when you've explicitly done a backup?
As it happens, you should be able to use the "Rebuild users" rebuild in the Admin CP for this specific case, which is lucky, but unfortunately we'd have no way of knowing if there is other data which has been affected.
Luckily we may be able to help you fix this retroactively but, seriously, we don't give people these warnings for the sake of it. It really does matter.