Is this the only tube of your spares that the patch cracked or are some of the others the same? I have never had this problem before. I patch tubes months before they get used, roll them up, sometimes with the patch folded and no problems. I do use Rema patches and fluid as they just seem to be the most reliable. The tube gets kept in a plastic bag in my seatpack mostly just to keep it from getting damaged from the constant rubbing that goes on in there. I know some here swear by using rubber cement, but my experience is that you can get a long-lasting patch sometimes but is much less reliable than the proper paired patch with vulcanizing fluid. Your patch has some mystery problem and IMO should just get a proper patch kit and spend your time riding rather than trying to figure out what went wrong.