Sounds like the EDL is not operatig and so not slowing down the spinning wheels.
The centre diff is what I would call slightly self-locking if there is a torque bias between front and rear but probably not enough to overcome rears on very slippery surface and fronts on grippy surface (when the EDL is inoperative), but
try giving more power, as soon as you ease back, the locking limited-slip/ self-locking-function is greatly diminished.
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