For some reason quad9 DNS servers don't resolve the domain (I'm guessing you're using those, like me?). No idea why.

Yes, Quad9.

Apparently it is blocked due to being part of DOMAINTOOLS hotlist https://www.quad9.net/result?url=contrachrome.com

I just used the form to report a false positive.

I believe that you can use the "no malware blocking" settings in order to avoid occasional false positives like this one: https://www.quad9.net/service/service-addresses-and-features

update: after I submitted the report, Quad9 have unblocked the domain, in under one hour! They are very responsive!