When in surround modes like Dolby Digital 5.1, 90% of watched television for me comes out of the center only because most TV shows (and movies) that are dialog heavy almost always mix the dialog hard center. In a sense my L and R speakers seem as if dead most of the time, but it's really just the source, not my system. Sorry if you already know this, but I thought it couldn't hurt mentioning.
Next time this happens, here is a helpful diagnostic test:
Run a manual speaker setup where you can manually move the pink noise around to each speaker. Don't worry, you won't muck up any Audyssey tests as long as you don't change and then lock in any adjustments.
Menu> Manual Setup> Speaker Setup> Channel Level> [ get ready to turn your volume down in a moment, the next step is kinda loud, and unnecessarily so for our diagnostic test] >Test Tone Start> *use the up/down arrows to move the test noise to all speakers.* Exit test by hitting Menu.
If all the speakers worked and corresponded to the one shown onscreen, then we know everything works , but either the incoming signal is L & R channel info shy, the Multichannel analog in L & R connection/wire/source is absent (if you are using that port), or there is some weird mode on the AV7005 (I can't think of) that kills the L & R channels but preserves the rest. [or something is intermittent/broken]
edit to add:
Are you using any outboard amps or subs that have an "auto" (turn on) mode, by chance?