VM Proxy NIC confusion

While trying to find a good use for my second NIC port (suggestions welcome), I started testing moving docker containers & VMs to the second port. Purely for testing/learning at this point. I've been trying to get VMs to work for far to long and feel like I've exhausted my knowledge.

What I have setup currently:

my Unraid server has 2 NIC ports (eth0 and eth1) with bonding disabled for both, bridging enabled for both. eth0 has an IPv4 address assigned automatically by my DCHP server (a pfSense router). eth1 has no IPv4 assignment. Everything is networked through an unmanaged switch. I'm currently using the binhex-delugevpn docker container to act as my privoxy proxy server. The container is on a custom docker network, which I believe to be routed through eth0 (i don't know how to check/verify this). I have a few different Virtual Machines running on my Unraid box. Until this testing, all have previosuly been connected to the network bridge br0, but when switching them to br1, I'm running into proxy issues.

What I'm trying to do:

From any of the VMs, if I disable the proxy, i can reach the internet. As soon as I enable the proxy connection by specifying my Unraid server's IP address and the Privoxy port, web browsers no longer load pages. With the proxy settings turned on, I can ping my Unraid server fine. I can also ping Google.com fine as well, but the page won't load in a web browser. I can't access any other docker's WebUIs as well with the proxy turned on in windows.

From other computers on my network, i don't have this issue using the proxy. If I switch the VM's network bridge to br0, I don't have any of the described issues when connected via the proxy. My guess is communication between eth0/br0 and eth1/br1, but I'm not sure where or how to test/verify/address that.

At the moment this exercise is just me learning how this all works. I can put everything back on eth0/br0 and run just fine, but I'd like to understand why this doesn't work and what I'm overlooking. Not sure yet if there is any value even in moving a VM over to eth1. Any help/documentation would be greatly appreciated to help scratch this itch!