I'm surprised nobody's called you on this, but are you sure you don't mean TAIL heavy? You put everything on the nose, including an extra 3oz of lead, which means the plane was either really tail heavy to begin with, or you're doing the wrong thing to correct a nose heavy situation.

One thing that can make a plane want to snap out of a loop is too much elevator throw. Any plane, no matter where the CG is, will snap roll if the elevator throws are too high.

The TuffFlight guys (I fly against the actual designers/manufacturers of the Predator in several meets each year) are flying theirs on the ragged edge of snapping all the time. When they get a couple of streamers loaded up, they have to be really careful.