Oldie but googie

The application folder contains most of the program parts, other than drivers & dll's.  It also has sub-folders with various additional components.  One such folder is Settings.  The three files that are typically deleted for diagnostic purposes are MC State, Site Settings, and Site Attributes.  These will rebuild as needed.

The Avid User folder contains each individual users settings, with each user in a separete folder..  For diagnostics, I usually recommend just creating a new User Setting,.

The Avid Project folder contains your various projects, within their own folders.  Within each project folder is your project data. settings, Bins, etc..  Media is stored separately.  In each project folder there is a project settings file.  It has the same name as the project, followed by "settings", and an extension of .avs.  You can delete this file for diagnostics.

Because all these settings are loaded into RAM during launch, they are all subject to corruption.  Therefore, for diagnostics, it is best to delete all the files at the same time.  Otherwise, a new settings file may become corrupted by one that wasn't deleted.  Not deleting all 4 files, and creating a new User Profile, doesn't provide a pure scientific result.

To summarize:  In the Settings folder, delete MC State, Site Settings, and Site Attributes.  In the Project folder, delete the Project Settings file (.avs).  For the User, just create a new User Profile as you launch Avid, after deleting the other 4 files.