You have a much better chance of getting hit by lightening than a flying magnet mount and chances of getting hit by lightening is pretty darn slim.
Strangely enough, I have been hit by lightning (my daughter witnessed it) and my dual-band single-mag-mount antenna flew off my pickup half a dozen times before I finally gave up and threw it into the woods on the roadside after the last episode.
I have had several near misses but never been hit by lightening. As far as your mag mount problem, it is like I have said all along, if you you the CORRECT size magnet mount for the task at hand you will not have any problems. If you do not problems can ensue. All in one antenna/mag mount packages usually cut corners on size of magnet.