From Apr 28, 09:09 UTC Zaraz was failing and causing some domains to return a 500 NGINX error.
I disabled Zaraz entries on my domain around Apr 28, 09:37:00 UTC and Cloudflare disabled Zaraz for everyone around Apr 28, 09:52 UTC.
I’d really like to know what happened. If not a post here, at least an email to domain-affected owners.