There is an active disucssion going on in the Apple community forum that you may want to follow as well. I am still investigation this sisue to see if it's an issue with Canon's Bonjour implementaiton, an issue with OS X or an issue with my WiFi system.
Again, a 'fix' is to use a hard-coded IP address and the LPD protocol, but that's less than ideal because it means I need to configure my router to always handout the same IP address to the printers (or to not assign IP adresse in the range I configure the printers to use a static IP in). These printers will periodically go offline with both Macs. The RAX120 is a large router, so it takes up a lot of space on your shelf. This is a powerful, 12-stream router that is high performance. If you are looking more for a WiFi 6 standard that works well with Mac, we suggest the Netgear Nighthawk AX6000. I am having other issues with Canon printers (MF733C and 6230) connected via WiFi and using Bonjour. Netgear Nighthawk RAX120 WiFi Router WiFi 6 Standard. For my small office environment that was an adequate solution but it was way more work than I had hoped for. We tested the following steps in macOS 10.12 Sierra, and these steps work the same way for all versions dating back to OS X 10.7 Lion, though it will be listed as a WiFi Address in older versions. I 'solved' the issue by hard-wiring the printer to my Ethernet switch and using the Canon IJ Network protocol. I have this printer and have both Sierra and High Sierra and have experienced the 'printer offline' issue when the printer is conncted via WiFi and using Bonjour.
