2021 Version PU2 - USPS feature returns "Server commited a protocol violation. Section=ResponseStatusLine "

Hello,  we're planning on going live with the 2021 PU2 version on Friday (Upgrading from 7.7/2015).  When we try to validate an address using the USPS feature we get an error "Server committed a protocol violation. Section=ResponseStatusLine."

I'm not able to find any documentation or posts regarding this issue - any help you have to offer would be appreciated. Its a possibility the server can't reach the server due to network communication restrictions, if that's the case, what is the website/server information it is trying to access so we can have it whitelisted?