I have a strange problem and I am not sure it is isolated to Deco XE75 Pro, it could also be related to Omada ER605.

I have Omada ER605 router set up as the main router and DHCP server. I have two Deco XE75 Pro set up as access points. There is a 5 GHz network and a 2.4 GHz network set up with different SSIDs.

I have two 3D printers running Klipper firmware, Moonraker software, and Pi OS Lite on two different Raspberry PIs: one is Pi 3b with only 2.4 GHZ wifi and the other is Pi 4 with 5 HZ wifi. I access these 3D printers over the local network using their static IP addresses.

What happens is that after some time I cannot access the Pi 4 printer (connected to 5 GHz network) from any 5 GHz device. It happens after some random amount of time of network running normally. I can access the same Pi 4 printer over LAN and I can access the Pi 3b printer (connected to 2.4 GHz network) from either 5 GHz device or LAN. I also have OpenVPN set up and if I connect over mobile network over VPN, I can also access the Pi 4 printer. But unless I reboot the Deco XE75 Pro, I will never be able to access the Pi 4 from any 5 GHz device.

Why is this happening? What can possibly prevent devices on the same wireless network (only 5 GHz) not to be able to connect to this device while LAN and 2.4 GHz devices work? Is this something to do with ER605?

To clarify, if I simply reboot Deco XE75 Pro, it all works fine. I don't have to do anything to ER605 but only to XE75 Pro.

What is also strange is that the same issue used to happen with my very old WDR3600, except that with that device I could not access the same printer even over VPN (could still access over LAN). I would have to reboot WDR3600 and then all works ok.

Can anyone help fix this issue?