Have you thought instead of Global Proxy , try to test it with “VPN policy based on client device” and test it with one device at a time ?

Global Proxy works fine for me on Flint 2 though.

Also are you using Flint 2 in addition to your home router ? So are you double NATing ?

It would probably help if you showed the diagram + IPs for your LAN via something like https://draw.io/ , but take out important IPs and such.