The port forward was failing due to a routing issue caused by the oVPN client connection. The baseline config documented by the provider had not mentioned that it would pull routes for the below and I hadn't noticed:
0.0.0.0/1, 128.0.0.0/1, 2000::/3
I had masked the issue by explicitly defining the gateway used by outbound Rules. Once the option "Don't pull routes" was enabled in the oVPN client config, the port forward was happy and the gateway no longer needed defining in Rules. I've requested of the oVPN provider, PIA, to include this as a heads up in their guide....and now I am more aware of the routes.
The webserver's response now shows as expected from the internal interface.
[image: 1616549857857-outbound.png]
Thanks to @its_maek for documenting their findings in this netgate forum topic!
VPN Server from Private Internet Access (PIA) created a route 0.0.0.0/1 when the interface is created.
In OpenVPN client I had to select "Don't pull routes" and it no longer makes that route. pfSense 127.0.0.1 now properly goes through the default Gateway.