There are only two possibilities:
- Either the IconCache folder or its contents have been deleted or is unreadable
- An app or utility on your PC reset all folders to their native state
Bear in mind that reinstalling Windows will also reset all your folders to their native yellow state.
We believe you found the cause of the issue, namely due to Google Drive. There is not currently a way to force folders in Google Drive to retain their custom icon as per the desktop.ini within those folders. Our team is studying methods to restore these icons, but at this time it looks like it’s going to involve a manual restore. This is due to how Google Drive operates, and does not specifically relate to our app. We will let you know the moment we have a potential solution!