If you're flying on the chair attached to the drone and you throw something from your inventory, it will unseat you from the drone.  Multiple tests seems to happen about 80% of the time.

I just tested and wasn't able to reproduce being unseated, but I did notice the drone would reduce altitude if the dropped item collided with the drone. Whether this happens depends on the velocity of the drone and where the player throws the items. It's easier to reproduce in passenger/hybrid mode since the player can angle the camera downward to throw items closer to the drone.

There are multiple reasons that a drone can be moved as a result of a nearby object.

(1) The drone was simply pushed aside by the dropped item (Unity Engine collision).
(2) The collision briefly "disabled" the drone (0.25 seconds).
(3) The collision caused damage and therefore briefly "disabled" the drone (0.25 seconds by default).
(4) The drone performed a "sweep test" which found the dropped item nearby and considered it a surface which could be landed on so it forcibly descended.

I tried to narrow it down by blocking collision disabling (2), blocking collision damage (3) and blocking the landing behavior (4). It mostly resolved the issue but the drone would still react a bit when dropping larger items, which I think is due to simply Unity Engine collision (1).

I think the best place to try to mitigate this issue is in the Better Drone Collision plugin, so I have released an update to it to mitigate (2) and (3). It doesn't seem like I need to do anything for (4) as I don't think the dropped items are detected by the sweep test.