Offline cameras

Hints on way to resolve cameras that go "offline"?  I had one that would waver between online and offline without me changing anything (and it's located no further than 20 feet from my router) and unfortunately it missed some pretty important footage as my garage was being robbed. Now that camera consistently stays online but my backyard camera goes offline and online at different times - and again I have changed nothing in their locations, settings, router location or anything. Even when it indicates "offline" in the app, if I click Live View about 80% of the time it will click on to the Live View but I'm afraid since it's offline it won't be triggered by motion and miss something important - like my garage camera seemed to do. Any advice is welcome.