Yes, I have seen this.
Inspect the ECM/controller cover for damage from battery leakage.
The Toyota battery tray can allow battery acid to leak off its left front corner and drip directly onto the ECM/controller cover below the tray.
Acid WILL eat a hole in the cover if the condition is not caught and corrected in a timely manner.
Once acid has created a hole in the ECM cover, acid will then enter the ECM enclosure and as fate/design would have it, the acid can then track right down the seat switch harness to the multi wire latching connector where it will spread out along the wires and corrode and/or contaminate the whole works.
Most of the incidents I have encountered with this had symptoms where the trans drive would disengage as if the seat had been vacated, but the seat was still occupied.
Have not run across any cases of the transmission just spontaneously jumping into gear of its own accord.
Are you seeing any trouble code on the multi display monitor?
If so, what codes.