A corrupt configuration file can disable HK downloading even when it shouldn't.
curl -v http://hkdata.makemkv.com/hashedkeys.txt
If you get a redirect or error, the server may be temporarily overloaded. makemkv automatic hk downloading is disabled or failed upd
If the servers are temporarily down (which happens occasionally during high traffic or maintenance), you can often bypass the check by using the File > Open Files method rather than the automatic disc detection, though this is less reliable for brand-new discs. A corrupt configuration file can disable HK downloading
Alternatively, if you are trying to open a UHD disc, ensure your drive is actually UHD-compatible. If the drive firmware is "friendly" (revoked), the automatic download might fail because the drive itself is rejecting the command. If you get a redirect or error, the