Port Forwarding not working on Deco X20
I previously had an old AirPort Extreme. I had it set up to forward ports to two machines: an iMac and a Pi4. This worked brilliantly and enabled me to ssh to either machine from anywhere. It also enabled me to set up reverse ssh tunnels from a couple of remote Pies to my iMac. This also worked brilliantly.
Then I replaced the AirPort with a Deco X20 in router mode. Now port forwarding doesn't work at all. I can no longer ssh in to either machines and the ssh tunnels no longer work.
I have set reserved IP addresses for both machines. I have forwarded external ports to port 22 on each machine.
This is exactly how it was set up with the AirPort Extreme. It worked. It doesn't work with the Deco X20.
What have I done wrong?