3x Untangle 16.1.1 servers
Windows 10 clients PCs
Various versions of OpenVPN client

We have had a strange and sudden change in how DNS works via OpenVPN in our environment. Prior to a couple of weeks ago DNS worked perfectly for our remote users. When they made DNS requests for resources inside our network those requests were serviced quickly and correctly. A couple of weeks ago something changed this. It started with a few machines then over a few days eventually encompassed all remote PCs. DNS queries for internal resources went unfulfilled. All DNS traffic suddenly was only sent to DNS servers that were not a part of our network and thus did not know what the DNS name of internal resources translated to.

Internal DNS servers were still reachable. Both via ping and NSLookup and those same servers are listed on the TAP interface. Yet DNS queries no longer go down the VPN tunnel and this resources such as our remote desktop cluster that makes use of round robin DNS responses goes straight to one server (had to add to hosts file to get it working for now).

Did OpenVPN change or is this a Windows 10 change? Is there a way to fix this?