Sometimes 1.1.1.1 is used as a testing value, and can get blocked for reasons. CloudFlare is getting a huge amount of spam IP traffic to 1.1.1.1 from misconfigured equipment, it wouldn't be too surprising if some upstreams have firewalled valid IPs.
When cloudflare resolves addresses, the DNS request is not coming from 1.1.1.1, it's coming from the IP address of the server actually making the request. You can confirm this by looking at the results of a VPN DNS leak test [0] and seeing the IPs being used to resolve the addresses do come from cloudflare, but are not 1.1.1.1