This article applies to the customers using Power Apps component framework preview feature on canvas apps. If you have this preview enabled and have added code components to the app between version 3.25002 (mid-May 2020) to 3.26005 (mid-July 2020), opening these apps in Power Apps Studio will show following warning.
Canvas apps internally uses ordered list of enum values to identify various types during app import and control creation. With the new property addition in version 3.25002 a bug got introduced which altered this ordering and affected all code components.
Apps created between version 3.25002 and 3.26005 will show above error message. There is no automatic upgrade handling for this preview feature (https://aka.ms/PCFBlog).
Clicking Open app will remove all code components and you will need to add the code components again. You can find more details on adding code components to canvas apps here.