Apps not opening "Verifying"
If you are sure that you downloaded the app installer from the official/verified source and that it has not been tempered with, you can skip the verification process altogether by removing the extended file attribute that causes FileVault to attempt to verify the application. Do this by executing the following command from terminal:

xattr -d com.apple.quarantine /Applications/app_name.app

The app_name.app is the name of the application you are changing the extended attributes on. In this case, GTA5.app.

The xattr command allows you to view and change extended file attributes. The -d flag indicates you are deleting the com.apple.quarantine attribute which is set on the application package. Any file with the extended attribute of com.apple.quarantine is verified by FileVault. This attribute is typically automatically set on downloaded files and files extracted from a tar or zip archive.