I just did this manual workaround for one of my members that worked....
They had messed up their password when trying to sign up for a membership site. They clicked the forgot password link but never got the email. Checked their spam folder - no joy.
When I went into my list of contacts, their name showed up under All Contacts, but not under Members. I clicked their name in that contact listing there, and then used 'delete profile' .
I then instructed them to open a private window / incognito window on their browser and manually enter the sign-up URL in that address window, rather than clicking on the link I had provided them (to assure it would be opening using the private window) - I recommended this as a shortcut/easy way to have their browser ignore their cache, rather than instruct them how to clear it.
Anyway - they went to the sign up page and then had no trouble starting the process from the beginning, with ease and success.
Good luck - hope this helps