Hi Mike,
I hope we can get some clarity into this with all of us remaining sane. 
My guess would be that when connected to the VPN, there is a corporate firewall at the end of the tunnel that happily replaces any SSL certificates in order to inspect network traffic. You’d recognize this by “PKIX Path building failed” errors in the console view when installing extensions or running e.g. a GET Request node.
If that is the case: to get around this limitation, checkout the below thread (I’d try the knime.ini parameters first, as that is quick to check).
Kind regards
Marvin