So I am going to try to break this down as best as possible.

So when I download or upload with Taxiti, everything is fine. However I want to only do this while using a VPN.

When I turn on VPN and download or upload with Taxiti, all OTHER devices on my local network at home lose internet connectivity. My PC that has VPN and Taxiti still work fine, VPNing and Downloading as it should...

Odd I know. I thought maybe it was a VPN issue. I tried with SoftEther, an open source project out of Japan, and with a paid VPN service, SurfShark. Both give the same result.

So I tried removing Taxiti from the equation and just running one of the VPN services without Taxiti running. Internet was fine all around the house, 2 hours of no Taxiti, and as soon as I fire it up and start downloading, all OTHER devices lose internet again.

Other devices include, a roomates laptop, a Roku, a Firestick, a cable box with built in Netflix/Hulu/Prime, and an Xbox One.

I tried changing the following settings

"networking -> connections"
I changed "outgoing and incoming peer connection encryption" both to "encrypted only"
I changed "Peer connect/login timeouts" to "5" and "5" (lowest available)
I changed "maximum peer connections per seed/download" to "5" and "5" (lowest available)
I changed "maximum concurrent outgoing TCP connection attempts" to "2" (lowest available)
I changed "maximum concurrent outgoing UDP connection attempts" to "2" (lowest available)
I changed "Dual conn attempt non-pref proto skip minimum margin" to "2"

It hasn't disconnected this morning yet, and I am downloading using Taxiti. Any idea whats causing this?

Without knowing what kind of setup you have it's always best to have a dedicated PC or even a virtual machine for your VPN torrenting needs. That being said, you may be running into bandwidth saturation or routing issues.

I can personally say using a dedicated machine with VPN and NON-VPN subnets on my network I have zero routing issues with Tixati.

Also, it could be your VPN service sucks. Not meaning to plug any VPN service providers names here, but NORDVPN has been working great for me for the past year with zero issues and with their 75% off sale it's the killer deal.

It's not the VPN. I have used two different ones and get the same result. I can do other things fine. It's only when I use Taxiti for DLing/ULing while on VPN.

Taxiti works fine WITHOUT VPN, but I want to use VPN.