Not sure why setting one of your uplinks to a static IP prevents you from pinging an address on the Internet.
I have 2 uplinks and both use static IPs assigned by the provider and everything works fine with or without firewall.
Are you doing all these diagnostics in ZS console or from a machine on your LAN? I would run diags on ZS directly using ssh first.
I am accessing ZS console from a machine in LAN (web access). And I diagnosed all these on some machines in LAN which have Linux MAC and Windows OS. They are showing same results, the issue is with Static IP no firewall issue.