email not saving

Hello!
For my custom post type, when a user adds in their email address, it doesn’t save. I’ve tried making it a mandatory field but that’s not worked.
I was searching through the old support tickets and saw that someone else had this issue back in 2015. You didn’t write how it was fixed, only that you had fixed with. It was an issue with some kind of corrupt table (?)
Website is http://www.bookastall.com and it’s happening with the people who add their own Stallholder listing at the £35 level.
I’ll add my credentials in the next email.
Thank you
Yvette