An Error Can Occur When Creating or Editing Custom Lightning Record Pages in the Lightning App Builder

In some cases, if you get the error while editing the page via the Edit Page option in the Setup menu, closing it and editing the page from within Setup can work instead.

If you continue to see the error, it is likely due to a suspended managed package which includes a global action. When the Lightning App Builder loads a record page, it loads every global action in the org, regardless of whether the action is on the global publisher layout. This includes actions from suspended managed packages, so if a global action is associated with a suspended package, you can run into the error. 

We recommend that you review existing suspended managed packages in your org and remove those (or their associated global actions if possible) that are no longer needed.