Do you have any custom codes added to your site? Would it be possible if you could share temp admin access so we can check? You can post the details here using the private reply option below.
That’s really a weird issue you’re having there! Can you try deleting the plugin, download a fresh copy of it on your Accounts page, install and activate it and see if you get the same thing? Actually, can you do the same thing on both the theme and plugin then check?
As you have built your page with the BB page builder, this means the issue is recent. Have any changes happened to either your site or server recently that you can think of?
Did you backup your dev site and hand over the backup information for them to restore? If so, then they’re going to want to follow the instructions on the link below.