I make my own pre-glued patches out of my old innertubes...
chop up old tube, sand it, put the rubber cement on, let it dry a minute or so, put aluminum foil on it.
Haven't ever failed.

Are you remembering to sand the hole and put rubber cement and let it dry Before applying the patch?
Rubber cement is a little counterintuitive from other glue in that you want it to be dried before sticking the two pieces together...