Actors briefly walk in air

Any idea why some of my actors briefly walk in air? There is no apparent reason, no physics.

Actors are based on a child blueprint, overlap events only on pawn Capsule to query dynamics.

Video


Update: Moving the Nav volume seems to address this issue, but still happening.

Bug report https://answers.unrealengine.com/questions/535283/possible-bug-affecting-actor-nav-when-landscape-is.html