My team and I recently ran into an issue with curl where it would randomly error out with "host not found" when trying to ping a specific URL.
Here is how the Cycle team described it to me:
"it's a race condition that exists within that version of curl where it doesn't know what to do when it gets a "no ip found" for ipv6"
While this has been fixed in newer versions, those aren't available on our version of Debian.
As a workaround, we've added a custom DNS resolution record for that URL in the Discovery service in Cycle.
I hope this helps anyone else facing the same issue! Thank you to the Cycle team for your help with this.