Router blocking printer visibility

I've set up two Epson printers on wifi. They work when first set up, but after awhile, NO computer or phone on my wifi network can see the printers. It's like the router is blocking them. I have restarted everything (router first, then printers then devices). Sometimes this magically works, but not always. I have removed and re-installed the printers (sometimes this magically works, but not always). I have disabled Advanced Security on xfinity. I have disabled Guest Mode (which is too bad, because I find that useful when I'm out and about and would like to contribute to the greater network). I have separated my dual-band wifi into two access points, and confirmed that all devices are using the 2.4. I have confirmed that the printers can be seen on the router as connected devices, and the IP addresses haven't changed in ages. I can print to these printers directly via USB, so they do print. Can anyone help? This is super-frustrating.