Epson Printer will no longer communicate with iMac after software update.

Reset the iMac's Printing System and then Re-Add the Printer.

see > Reset the printing system on your Mac to solve a problem - Apple Support

Go to Privacy & Security > Local Network > turn on appropriate choices including raster….

allen ski wrote:

I updated the software on both my iMac and the printer.

I recall something like this happening in the past (it has not happened to me with 15.3 but I think with an earlier version of MacOS). I have a Canon printer from 2010 and an Epson printer from 2015, so these are pretty old devices but they still work under 15.3 for me. When I encountered this, what I did was remove the printer from Print Center and then completely remove all the software associated with the problem printer. If there is an uninstaller, that is best, but one can manually remove all the software pieces by using Find Any File (which you can download) and searching for certain character strings in file names and contents. Be sure to include hidden directories in your search. Then restart. Then I installed from scratch the printer software. It then functioned properly on the network.

Can you see the printer's web page?

Find its IP address and try to open it with a browser. That will show whether or not it's actually on your network

The IP address should be findable through the printer's info panel under settings or network or maintenance.

"How can the printer be visible in the printer list but also be 'offline'? " If your printer were turned off then it would be offline but the drivers are still loaded.

If your firewall is turned on then try turning it off (System Settings - search Firewall).

I assume there are no error messages on the printer panel.

Printer is turned on. Firewall is turned off.

janomo2 wrote:

Now I restarted the router and suddenly none of my two printers (Epson NX420 and Brother HL-5470W) can be found anymore to connect. — How can I go to that “rastertoescII” to switch on? Cannot find it anywhere...

If you restart the router and a printer no longer can be found to connect ... it is possible that you have to manually connect them to the router/network again. I have two printers, one 15 years old the other 10 years old, and one of them does not "log in" to the router automatically if the router is restarted. For that, I can power down the printer then power it back up and it logs in with the stored password, or I can go through its setup and re-log it back in to the router manually.

Absolutely the same problem and description, same printer but on iMac. Deleting the printer, reinstalling... the printer shows up as recognized, idle, the print monitor is active... yet nothing happens. Restarted the printer, the connection, removing and adding the device... still no printing. But scan works.

Now I restarted the router and suddenly none of my two printers (Epson NX420 and Brother HL-5470W) can be found anymore to connect. — How can I go to that “rastertoescII” to switch on? Cannot find it anywhere...

Tried resetting the printing system, as suggested below. Re-added the printer. Still wouldn't print or scan. Repeated the reset procedure etc.. Same, still no print or scan. Rinse, repeat. Nothing. Switched the printer off and turned it on again. Reset the printer system again. Attempted to add the printer. 'Unable to communicate with the printer at this time.'

Where do I go from here?