@mer Thanks for the reply! Your comments got me to thinking which can be dangerous ;-)

I figured out the problem. It has to do with little Windows 10 app that the commercial VPN provides. This app resides in the system tray on the right side of the task bar in Windows 10. The app is used to connect and disconnect from the VPN. With your comments, I had the thought to try to figure out what DNS server windows was using when connected to the VPN and when not connected to the VPN. With a quick google search I found the Windows 10 command prompt nslookup command. Simply entering "nslookup" in a windows command prompt will return the DNS server being used. In my case, when I wasn't connected to the VPN, it returned the ip of my pfSense router. When I was connected to the VPN it returned an ip of a DNS server that belongs to my VPN provider. It seems that everytime you connect to the VPN service using their Windows 10 app, they change your DNS server address to their DNS server. I tried manually changing it back to the ip of my pfSense router but that didn't work when connected to the VPN - in that case I broke internet access altogether and couldn't connect to anything. When connected to the VPN, Windows wasn't able to resolve the local ip of my pfSense router. The solution will have to be to stop using the app provided by the VPN provider so that the DNS server that Windows uses stays pointing to my pfSense router. I had previously setup a gateway associated wiht the commercial VPN provider in my pfSense router. My solution will be to configure pfSense to route traffic from my Windows 10 through the VPN gateway when I want to use the VPN from my Windows 10 pc. Sort of a pain b/c I will have to log in to pfSense every time I want to use (or not use) the VPN. But in this scenario I can use the https://server1name.domain_name.tld paradigm to access my local services from my Windows 10 pc whether or not its WAN traffic is being routed through the VPN. This is because my Windows 10 pc will always be configured to use pfSense for domain name resolution.