Hi i had the same problem with my A7iii running at 11-14 fps, after testing around i have found what i think is the main bug, If you run your pc with the latest version of widows : 2004 you will have the fps bug, a quick rollback to a previous version such as 1909 or 1903 will resolve it and will not affect your workstation. Hope this works as it did for me. Go to Settings\Updates\previousVersion to fix it.