Fix Wordpress membership site custom post type permissions errors

Hello freelancers, I have a website that needs URGENT attention. It is already live. The website was created mostly by another developer, here on freelancer.com, and now it's broken and he has not responded for 3 months. I am looking for someone willing to take over the development and work with me IMMEDIATELY, in the next 2-3 days. I can explain all the errors to you and give you full access; I'm available on Skype and WhatsApp. The project, in short, is a membership website built on Wordpress, with some plug-ins including "Custom Fields" and "Members". Each WP user that has the role 'member' is assigned a custom post type named 'listing'. In the administration, each listing is assigned an owner, which gets assigned to the member, so that the member can edit their own listing. However, going into the listing edit screen logged-in as a member and trying to click "Update" shows an error "You are not allowed to edit this item". Plus, then the custom post ownership gets reset to "0/Administrator", basically revoking privileges for individual members to edit their listings. I need this solved and I imagine it requires some amazing custom PHP programming skill, as well as understanding of Wordpress programming. If you can help me, please start your bid with "I can help" just so I know you've read this initial quick briefing. Thank you!