Well, typically 1.1.1.1 responds to pings. So it not responding is an indication that it's no longer working.

Or that it started filtering ICMP. If DNS works then it’s doing its job

Though the reason everyone started pinging is because DNS wasn't working

... or a change of policy, funky firewall or whatever.

It does seem to be responding to ping again and since my edit above, the first packet is being responded to so I suspect a NOC is having a fun old time somewhere.

You do need to test the service properly. I do this malarky for a living 8) I'm ever so popular with kiddies and their gaming related fixation with ping times ...