NOERROR and empty result for some *.proton.me subdomains

[GitStorageOne]

Hello,
spent the whole day debugging the problem - can't open https://docs.proton.me.

For some reason - no IP address.
Link to test quad9:
https://dns.quad9.net:5053/dns-query?name=docs.proton.me

Interestingly, there are no problems with domains like: drive.proton.me; calendar.proton.me; e.t.c.

Any ideas?

[GitStorageOne]

Seems the problem is with the Quad9 itself.