Its most likely that, as Denise said, the shift motor was stuck, usually the brushes for the motor get stuck so no electrical contact with rotor.
And moving it around, plus vibration unstuck it, but it is temporary, needs to be rebuilt or replaced, do not "count on it"
4low with an automatic transmission requires speedometer to be at 0MPH, foot on the brake and transmission in Park or Neutral
With Manual trans Clutch pedal must be down all the way, thats the same as Park or Neutral in an automatic.
Yes, the "steering wheels"(front wheels) are now powered so want to go straight not turn side to side.
You will also feel it lope as you turn because wheels are turning at a different speeds so differential is transferring power back and forth
You feel this more in 4low than 4high but the effect still there in 4high
This is why it is recommended you only use 4WD on loose surfaces, it allows the tires to slip a bit so you don't feel the effect as much as on high friction surfaces, i.e. dry paved roads
Low friction surfaces are snow, ice, gravel, dirt, mud, stream beds, ect.........