I have to turn off and on my WiFi every hour or so. What's wrong?
I agree that since your problem occurs over many devices it is unlikely to be a problem with the Apple devices. I appreciate your point about the Ubuntu device still appearing to work, but it still seems more likely to be a router problem (it could be for example the router is producing multiple errors that the Apple software is catching).

I'd suggest a hard reset of the router as Step 1 (before you do so however make sure you know ALL your current router settings, not just your name and password. I take a screenshot of each setting page)

Most routers have a Reset button you have to press with a paperclip.

Power off the router for several minutes, then apply power and do an immediate reset.