I've had a similar problem with Navi freezing sporadically. It typically stayed frozen when I stopped the engine and restarted immediately. But if I let it sit for a few minutes, it seemed to reset. Sounds like your problem.
I had additional issue that my sat radio went dead for minutes at a time, rarely. I had it serviced, they claimed they found a loose wire that might have been culprit but since problem is so rare who knows if it is fixed. Time will tell.