The decisive clamp: zero linear and angular velocity every frame for two seconds.
t=0.25 Z=3220 vZ=0 | t=0.75 Z=3683 vZ=0 | t=1.25 Z=4197 vZ=0
It rises at ~1200 cm/s with velocity pinned to zero, so this is not a force, an impulse, or a bad initial
state - all of those the clamp would have removed. Something calls a transform setter on the vehicle every
frame.
Our own source contains exactly one direct transform write outside the character (the shot actor's camera),
so the writer is engine-side: the Chaos vehicle component driving UpdatedComponent from a vehicle state that
was never created, or a skeletal-mesh transform update.
Also diffed the two maps, since the pawn works in ReviewMap and not in DemoMap: kill_z, gravity, lights and
partitioning are identical; DemoMap adds 593 static mesh actors, a height fog and a post-process volume,
ReviewMap adds a shot actor and the character. Nothing in either list can write a transform, so the map
difference is not in its actors or settings.