A possible cause for the registration error was shared here, it could be related to misconfigured mail server:
dprevived.com/t/the-more-than-two-people-in-a-thread-theory/80/post/448/
That would also explain the problem using the forgotten password form.
When this problem has been fixed, I would suggest that new user accounts are confirmed by e-mail before they are active, since there is otherwise no way to know if the registered e-mail address belongs to the poster or someone else entirely. Hence, other communication from the site may end up in the wrong hands. There's a Misago option for this:
misago.gitbook.io/docs/settings/dynamic#account_activation