Almost certainly, your problem lies with mDNS device discovery - or in this case, mDNS protocol not being forwarded between switch-ports and WiFi clients.
As described, your WiFi Router or Network Switch may be blocking this device discovery protocol. Apple Bonjour traffic, upon which AirPrint depends, uses mDNS. The Apple Bonjour protocol uses UDP port 5353.
You may find that restart of your network components will resolve the problem, but you’ll need to restart your network devices in the correct order. Assuming that you WiFi Router provides DNS services for your network (noting that whilst DNS and mDNS are related in their function, they are effectively independent of each-other) restart devices in this order - allowing time for devices to fully boot/restart prior to restarting other devices:
- WiFi Router
- Upstream wired Network Switch(es)
- WiFi Access Points / Network Extenders
- Other fixed infrastructure devices - such as Printers
- Client devices
Restarting your iPad, after restarting other devices in the correct sequence, is most simply achieved by a forced-restart of the iPad:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
If you continue to experience difficulties, you may need to review your Router settings. Unfortunately, different Router manufacturers use different terms to describe different features. Look for settings such as “device isolation” or “Publicly Secure Packet Forwarding (PSPF) - and if found, try disabling them. Likewise, IGMP Spoofing (if present) is a candidate for experimentation.
