I’m fairly certain this all stems from the mass robots.txt deletion and is actually hardly related to the issues that caused the WPM errors previously.
No robots.txt = no robots.txt blocking = new errors
When robots.txt went down we had 5,000 new pages get added to “Crawled - currently not indexed” and 4,000 new 404 pages.
This is turning into a whitepaper I’ll be calling “The Worst Technical SEO Nightmares and How To Make Them Worse” that I release when this is all over.