https://serverguy.com/case-study/cloudflare-seo/ . It is well known in the SEO arena that your neighbors affect your SERPS. Cloudflare has an open policy on who they allow on their service where AWS, Akmai, Fastly, etc have acceptable use policies banning services like online gambling, online pharmancies, etc.

Google doesn't release any information about how they rank sites but it is reasonable to assume there is a network/IP reputation score similar to what email providers use to combat spam.