IPs blocked? Connection to api no more possible

We have had a few cases recently of networks that couldn't route to (or otherwise blocked) the IP because 172.65 is near the private IP space and systems were misconfigured to think that it was part of that block too. It would seem a bit odd if ping works and 443 doesn't, but it could be a firewall blocking TCP and allowing ICMP or something like that. Just something random to look into because it seems to have come up lately.