Many times sharepoint designer gets stuck/ Considers checked out files as checked in or vice versa.
In most common scenario you’ll see a message like “Cannot perform this operation. The file is no longer checked out or has been deleted.” while checking in a file.
The solution is to clear all the cache that SharePoint designer has stored on your machine.
For clearing that you can press Win + R and navigate to these two folders and delete all available files.
- %APPDATA%MicrosoftWeb Server ExtensionsCache