Littco
It is usually the way it is added! Spray cans were the best as it spray fed into the fuel on filling but they were a pain and tedious
Many are now pour cans and its very tempting to tip the lot in one go.
Fuelers won't touch the stuff normally but saw one filling an aircraft where the crew were still sorting paperwork inside the aircraft he filled it then poured the tin of Prist in afterwards
it is pretty lethal stuff if not added carefully
Assuming a/p was engaged after t/o, could elevator trim failure be more indicative of loss of control.
Its unlikely that the autopilot would be engaged until the aircraft was fully cleaned up. Takeoff flap is usually the last to go and not till 400 feet agl so AP not till 500 feet or later. No PAX and just crew and its fun time to hand fly so maybe much higher than that. First sign of a control problem and auto is the first to disconnect
Pace