I had the same problems with a previous Canon printer. Searched and searched the internet for answers with no luck!
Reset printer to default settings and set back up Restarted both MacBook and Printer multiple times Printed Network status sheet directly from printer and it tells me my connection is EXCELLENT every time. Verified multiple times the printer IS on my network both via my WiFi router settings and at the printer. Uninstalled/Reinstalled the printer drivers etc, they ARE up to date. Removed/Re-added the printer from my MacBook Pro I check the internet connection status on the printer itself and it always says it is connected.
I have an Epson EcoTank printer that I am constantly having issues connecting to via my 2015 MacBook Pro.