Everything, just vanished. It must be 100's of files suddenly gone." Google has a post up on the Google Drive help forums more or less acknowledging the issue.

What Google said. “Clarified in the favicon documentation that both the favicon file and the home page of the site must be allowed for crawling by Googlebot-Image and Googlebot respectively ...

Google says the issue only impacted a “small subset” of Drive users on desktop using version 84. Hopefully, this solution can help get missing files back to users.