Hi @HannibalLecter,
We've checked the traffic and the ASN is allowed and has traffic coming through. But we can't see any traffic coming through from your IP so it might be being blocked somewhere else. Can you try using the --trace option to see if we can look into this further:
curl --trace - --trace-time https://artifacts.elastic.co/GPG-KEY-elasticsearch
If might also be worth looking to see if a firewall or other mechanism in between could be blocking the traffic.
Let us know if the trace option gives you more details and we can investigate further.
Hope that helps!