[ZeroAlphaOne]

I use to own a G&G CQB-R M4.

The problem you are describing is a common fault with that Airsoft Weapon.
You have to be extra careful with the sliding stock, otherwise you can damage the internal wiring.

You don't want to damage the wiring loom too much, otherwise you will have to rewire it to the mechbox, and its a bastard !
The wire seems to be a lot thinner than the normal gearbox wiring looms. The reason for this could be the very small hole in the stock pipe which the wiring loom goes through to the mechbox.

I agree with Mike624 in his advise / comment,

Don't put the battery in the stock from the front like the manual shows. Pull the butt plate off and stick it in from the back end and pull the connector through so it connects at the back.

That way your stock will collapse just fine without any wires getting pinched or pulled anywhere.

So unclip the two plastic clips on the rear of your stock and remove the but plate which gives you access to the battery. By doing so will reduce the risk of damage to the wiring loom and the connectors.