The process of discovering a printer on a wifi network uses avahi-utils which I don't think is in the default install:
https://openwrt.org/packages/pkgdata/avahi-utils
You can work around it by using static IP's.
Also, printers often have 2 network settings: infrastructure vs ad hoc. In ad hoc printing, your job goes directly to the printer. In infrastructure, the print job passes through the router. Ad hoc is also referred to as a "guest network" and frequently is a different network.