Picked up a few GC752XP to test. We use SSL decryption on our networks. The switches can't connect to Insight because they don't trust the MITM certificates. I reached out to support per the document at https://kb.netgear.com/000053885/Insight-can-t-connect-to-my-Insight-managed-device-that-is-behind-a... to find out what the FQDN or IPs are of the Insight servers to build exception rules and they said they could not help and told me to come here.
As a follow up, Netgear support now says they won't give out IP addresses or FQDN of the systems their own devices need to communicate with for 'security reasons.' A network security company like Netgear should understand why that doesn't make sense.
It seems clear i'll have to packet capture these myself at some point or return the switches.
