Not exactly clear to me what tests you're doing here, and I always favor careful testing before tearing things apart and replacing things.

"rotated both front wheels" - does this mean all 4 wheels were off the ground, AT in neutral, parking brake off? Does it mean AT in park, one wheel off the ground at a time? Something else?

I don't think it's clear from this description, and the answer will impact the correct diagnosis. Maybe the other advice you're getting here is from people guessing correctly about what you mean, but maybe not.

Basically, all the gears / splines / CV joints from the AT to the Transfer Case to the front/rear differentials to the inner CV joints to the outer CV joints, are supposed to be connected at all times. From your symptoms, it seems everyone agrees that there is an intermittent break in this mechanical chain somewhere. You need to find that break, and I think you should be able to do it without disassembling anything or starting the engine.

I think jacking one wheel off the ground at a time should do this. E.g., jack the right front wheel (only that one) off the ground, support with a jack stand. Try to rotate that wheel. It should not turn other than a few degrees of angular slop. If you can spin it, you know the problem is somewhere between that wheel and your AT. So then have someone spin that wheel while you get under the car and see what is moving and what is not. The place where the movement stops indicates the problem spot.

No problem there? Move to the next wheel. One slightly complicating factor is that since the problem is intermittent, you could find that the process of asymmetrically jacking the car like this will cause splines to engage or joints to pop into contact, making the experiments tougher to do.

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2001 X5 3.0i, 203k miles, AT, owned since 2014