By any chance have you used any clear or colored mylar type of tape to hold the receiver antenna on the outside of the fuselage? I've seen this be a problem several times. If so, remove the tape.

Is there any type of ground strap that runs from the plug wire that needs to be connected to a ground location on the engine? Di-electric silicone grease, available at most auto parts stores, applied inside the cap may also help. Make certain that the product is di-electric silicone, not regular silicone.

Check thw wires entering and exiting the switch. Is it a new one or one that has been used several times before? Replace with new.

Battery leads, new or old? check condition and replace if any doubt. Loose motor mount or landing gear bolt and/or nut? BTW, 700mAh is a bit on the low side for an ignition battery. I would be having some serious concerns after about 1/2 way through the third flight.