accounts break on email addresses which contain plus (+) symbol
In the screenshot below, I've received the "[/e/] Your test account/email @e.email is ready" email to the address containing the plus symbol, then followed the link to the page shown below, which fails with the error below after I fill in details. The details I fill in do not include an email address.
I can't be certain it was the plus symbol that broke it, but it's a common oversight in email checking regex (despite rfc specifying it), and after being unable to get the page to work I repeated the process using a similar length email address without a plus, and that was successful.
(I suspect the privacy conscious demographic are going to be more likely to have emails containing that character)