Having trouble with Snes netplay, auto-disconnecting

A friend and I are trying to get netplay set up, we’ve made sure we have the same version of Retroarch (1.15.0), our Snes9x core is up to date and we have the same rom (using Mario Kart for the test)

Although my router has UPnP on, I couldn’t get it to work with that, so I port forwarded TCP 55435, which still yields a UPnP error, so I changed “netplay_nat_traversal” to “false” and it stopped giving this error. (We’ve since tried with this on both true and false)

If either of us try to host, it says we connected to the host, but then immediately says we’ve disconnected. This is both with and without using the relay host option.

My friend turned on logging, here’s what he got when I tried to connect.

“[INFO] [Netplay] Queued tunnel link connection. [INFO] [Netplay] Tunnel link connection completed. [INFO] [Netplay] Connection slot 0 [INFO] [Netplay] Got connection from: “Xirix” [INFO] [Netplay] Xirix has joined as player 2 (ping: 176 ms) [INFO] [Netplay] “Xirix” has disconnected”

Here’s what he got when trying to connect to me.

[INFO] [Netplay] Connected to: “Xirix” [ERROR] [Netplay] Netplay state load with an unexpected save state size. [INFO] [Netplay] Netplay disconnected

Not sure what’s up with the save state error. To experiment we both deleted the savestates for Mario Kart in the save, and netplay folder inside save, but it just did the same error again.

I’m on Windows 10, he’s on Linux if that’s a factor. We have no idea what to try next so I thought I’d ask.