I don't think it ever showed up. Seems to me that maintaining torsional stiffness is a challenge for a trike. I think a lack of torsional stiffness along the length of the trike contributes to tendencies to fish tail under hard pedalling. I think you compound these tendencies when you add a one wheel trailer. The front axle is the only thing there is to keep the thing level.
Loads have to be conveyed to the front axle by the frame of the trailer and trike.
That is a lot to ask, especially if you lengthen the trailer and add a heavy, high load. This may be what happened to Zach. When I had the trailer oscillation while towing a BOB COZ with bike box on top behind the Dragonflyer it was relatively uneventful. I just applied the brakes and it straightened out. Compare this to one wheeled trailer oscillation on a SWB bicycle which can be very hard to control and just about send the vehicle combination off the road.