Last week I made this post regarding the Hardware NAT feature on the mt7621 devices including my Ubiquiti Edgerouter X working most of the time but not working other times, when I made my previous post I did not fully understand under what conditions it worked and under what conditions it did not work and it seems to me reading it now that my previous post was unclear. Now after testing it for a week I think I am able to better understand what is going on so I am making a more clear post.
My devices connected to the router use Hardware NAT whenever I run a speedtest or something like that (and am not connected to a VPN on the client device), in fact Hardware NAT seems to work flawlessly when the client device is not connected to VPN, however when I connect the client devices (NOT the router itself) to any OpenVPN or WireGuard VPN server, and then run a speedtest immediately after connecting, I can see that it also uses Hardware NAT like it is supposed to, so the problem isn't with Hardware NAT not knowing what to do with VPN traffic. But then, if I wait just one or two minutes, then run another speedtest on the same device while connected to the same VPN server, it does not use hardware NAT, it goes back to using software NAT. I believe the cause for this is that after the connection between the client device and the VPN server is open for more than a minute or so, that connection between the VPN server and client devices stops using Hardware NAT and instead goes back to software NAT. But it only does that for the specific connection on that specific device, if I disconnect from VPN on the client device and run a speedtest it goes back to Hardware NAT, and if I connect to a different VPN server, it uses hardware NAT for a minute or two before it goes back to using software NAT. This is not the intended behavior and I would like to know more about why this happens and what I can do to keep the connections going through hardware NAT regardless of how long the connection has been open. If anyone has any knowledge on this, I would greatly appreciate some input, thanks.