Rustproofing is not something we have to deal with down here in the south, so I know nothing about it other than pictures and very little reading…
I would think if it was a coating binding something up, that it would work it’s way through it and stop soon, unless it had affected the grease/lube in someway… But if it is just a defective part, then it will get worse which in turn will make it far more easy to find the issue at hand…
Still thinking it might be the slip yoke or similar on the driveshaft causing the issue rather it be rustproofing, a defective part or just bad luck…
To clarify in the “south”, rustproofing shops quit operating in the late 70s or early 80s, never stop any rust on Florida cars.
But improvements by auto manufacturers have helped immensely.
A friend’s late 70s Civic rusted a hole through the roof!
Whereas my 2000 and newer vehicles, no problem.
Any chance you’re inadvertently moving the mode control knob in the center console each time prior to this happening? That dial is easy to move and it doesn’t take much to switch from 2WD to AWD.
Have no idea what those things are but even so, no. My hands are on the steering wheel, not fiddling with other stuff. Again, “It happens randomly. Nothing I do makes it happen.”