Whenever MATLAB crashes unexpectedly due to M-lint, it adds the name of the MATLAB file that caused the crash to a file known as "MLintFailureFiles". This causes the red indicator to appear in the respective MATLAB file when it is opened subsequently.
To work around this issue, perform the following steps:
1. Navigate to the preferences directory. (This is the directory that MATLAB returns when you execute "prefdir" in the MATLAB command window)
2. Open the file called "MLintFailureFiles", and remove the name of the file that the red indicator is showing up in.
3. Save "MLintFailureFiles", and close it. The red indicator should no longer appear.