In case anyone stumbles across this, the problem was that the entity that manages .icu domains received an abuse report and suspended my domain.
This is strange because I only use the domain for personal experimentation and none of that is just for static websites. DNS records for mail are properly configured like all of my other domains.
I asked Namecheap what the reason was. They said none was provided and it may take some time to get a reply back upon requesting the info. I asked them to put in a request for the reason.
My guess is that I was just in a massive list of domains that someone started reporting. or maybe someone was trying to get my domain taken out so they could take it for themself.