Ours hasn't had that problem, but periodically the GPS loses sync and can't re-establish it. It wasn't until very recently that I had enough empirical data to see the pattern.
We usually leave our rig plugged in when at home, since we're usually out at least once a month, if not twice. It seems like if the radio has power applied for a week or two even if it's "off", that's when the GPS hangs.
Much like your situation, either turning off all 12v power (i.e., with engine off, turn off 12v disconnect for 60 seconds or so), or popping off the LCD panel for 60 seconds and reinstalling it seems to allow it to work again.
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