Do you have security on for your project? Check if your user has access rights to the page and the data.
Check your page has the access to your logged-in userrole. You can apply user permission for the specific page as shown below
attaching a ss of the same.
Most of the issues of non edit-ability and not visible issues in Mendix are solved by validating Access Rules. As we develop the application further we tend to add new Pages/Microflows and Domain attributes and miss to update security flow for them and hence end up in trouble. Always a good idea to validate Access Rules. Cheers!!