I have just pushed another patch for our domain resolver. There were rare cases where your domain's CNAME wouldn't be resolved properly - even despite the fact that everything was alright on your side. We haven't touched that code from the very first time it was invented - and it was ancient at this point.
Good news is that I was finally able to test it with my own domain - it works.
Possibly good news is that this change might make root domains and 4 level domains work. Although, these are still not official according to DNS specifications. And FreeFlarum still resolves for CNAME record only.
Hopefully this will save a lot of headaches