So we finally figured this problem out. Our security team requires all laptops...mac and windows to use Zscaler, and while working with them I found the issue.
In the Zscaler admin console, they had whitlelisted Apple's entire IP range of 17.0.0.0... however they had it set to 17.0.0.0/24 ...which is only 256 addresses.
I noticed this and had them change it to 17.0.0.0/8, and voila! All macs could see and download all updates.
What a big hassle. I knew they had whitelisted apple IP in the past, so never thought anything of it. But thanks now to my keen eye, it's fixed!
Thanks everyone who tried to help. I appreciate it your time.
P.S. Zscaler is the devil. don't ever use it!!!