Intruder Alert?

You may just have a router that for whatever reason, is not recognizing a device as having already been assigned that IP -- some corrupted DHCP lease file or something in the router. If your network configuration is pretty simple, you may just want to try doing a factory reset on the router and setting it back up, as k.panic suggested a few posts back. If it is a router/modem combo, just make sure that you have the ISP username and password and any other important settings so that you will be able to painlessly reconnect to your ISP.

Yeah, I agree with this. I have a feeling the router's got an issue.

Also, I've never heard anyone recommend setting up static IPs for mobile devices like iPads and iPhones, DHCP is a currently well-accepted standard just about everywhere. I really can't think of a reason I'd ever set up a network that way, though of course I'm not the say all and end all!

You mentioned IT people are like stylists; everyone says something different. I'll be the first to agree, and it definitely makes giving advice difficult because while many IT folk are very well-informed, there are plenty of others who are happy to make something up that sounds good rather than doing the appropriate research and legwork to make sure the solutions they're recommending are the best setups for the user.

I can see a sleezy IT guy recommending static IPs so it gives him an extra half hour of labor he can charge for when he configures it, just like I've had oil change places tell me my air filter needs to be replaced while showing me a dirty filter they keep behind the counter pretending it's mine. There are shady people and there are honest people and the internet makes it difficult to figure out who's full of BS and who's knowledgeable. People like to speak authoritatively just for the sake of being heard or being right, but ultimately it's just about getting things fixed and back up and running as smoothly as possible.

The next step for me would be to try to reproduce the problem with as few devices connected to the network as possible.

Most routers, when you've logged into them, will show you the MAC addresses of connected devices somewhere within the web interface. For mine, it's grouped together with diagnostics and logging, but it varies by manufacturer.

If you know you usually see the error on one computer, try to reproduce the problem with just that computer on the network. Put your iOS devices in Airplane Mode; turn Airport/Wi-Fi off on your other computers. If it still happens, I'd log into the router and see if there are any other devices connected. If there's literally nothing on the network but the router and a computer, you've at least narrowed it down that far. Try with a different computer and see if you can reproduce it. It's all trial and error and a lot of process of elimination.

If it's a fairly recent Canon, joining it to the wi-fi network is the same as joining a computer or iPod touch. It shows you available networks, you select yours, then spend three minutes spinning the dial around to punch in the network password.

You probably could set up a static reservation by putting the MAC in on the router, yes. Canons usually use bonjour to advertise themselves on the network, which is why it doesn't matter if it has a static IP, bonjour takes care of advertising the printer's location on the network instead. Basically by setting up a static mapping, the printer will still think it's using DHCP and will ask the router for an address, and the router will always assign it the same IP address. That's a perfectly acceptable setup, at least in my opinion. Then if for some reason bonjour isn't working and your computers can't see it that way, you can still plug in the IP and print.

I did read the entire thread. You did not make the intent of that statement clear. However, I seem to sense some hostility - I'm not sure why - so I'll bow out.

PamsPlace, my hope that upgrading my router firmware had solved the problem was misplaced. The problem still exists 😟
Back to the drawing board !