Name and Last Name not remaining in backend

Hi,
I asked a question about the add-on “add name to checkout” on 20th december at this page: https://www.paidmembershipspro.com/add-first-and-last-name-fields-to-the-checkout-form/
But my question is still awaiting for approval, so that’s why i’m asking here as well:
After updating wordpress and my theme, the name and last name of my users dissapeared from wordpress->users, before the name and last name were displayed for each user: not anymore after the updates of wordpress and my theme. How can i resolve this? Thank you!

The page I need help with: [log in to see the link]