I am having similar challenges with AirPrint once my MF741Cdw goes to sleep.
UniFi Dream Machine --> UniFi Switch Lite 16 PoE --> UniFi Switch Flex Mini --> MF741Cdw
Printer is assigned a static IP address.
iOS devices are on the same network segment.
When the printer is sleeping I can ping the IP, I can access the GUI, and sending a print job via IPP wakes the printer.
However, when it is sleeping it does not seem to be responding to mDNS (Bonjour) discovery as my iOS devices all report "No AirPrint Printers Found" when searching. Or maybe it is not advertising itself, I am not entirely sure how AirPrint works under the covers.
Sometimes waking the printer up manually will resolve this, other times a full power cycle is required.
