Sway problem need help

Simple fix: add 1100 pouinds of weight to the forward of TT axles,
I be more concern about the TT frame having additional overhang, not designed by the TT manufacture's engineers. Is your engineer familar with frame rails aka channel steel sizing and guage? What about ply rating of your tires,
Are they capable of additional wt?.
You should start by loading your TT as if your outbound. Take it to a public scale, and scale each axle and then the entire TT. Your TT will have a max load rating, make sure your not overweight. Also the axles have a max load rating set by the manufacture, make sure your within your axle limits. See if you can carry the additional wt. After comfirming the above load your HD and go back to the scale and repeat all and see if your max wt is within the TT limits and dont't forget to make sure yout TV isn't over it max load ratings
What's your TV?, can you put the scooter in the back? Have you seen others doing the same on thier TT.(I haven't seen that setup)
And lastly do you want your HD sitting on somthing that only has a 2 inch (the ball) connection to you?
Scrap it; either buy a little popup to tow behind the HD or get a truck as a TW (and if you already hve the Pick up then put HD in the back of it.

That "engineer" needs to go to a basic physics class. You unloaded weight on the tongue by loading weight on the rear of the trailer. The trailer is a basic fulcrum with the wheels being the pivot. Any trailer with not enough weight on the tongue will sway; the less weight the more sway until it is completely unstable and causes a crash.

It sounds like you solved your own problem. You stated that the Harley causes significant sway when towed with the trailer and goes away when removed from the trailer. I believe what you are experiencing is insufficient tongue weight, caused by the additional weight on the rear of the trailer. You might try lowering your hitch head a bit and installing an additional sway control device to see if that helps.

I am no expert but you need to check tongue weight with and without rack/bike. I doubt you have much tongue weight left adding that much to the back. I fear your only solution will be to scrap this idea.

Did you upgrade the trailer frame, springs, axle, tires, and wheels too? That's a lot of added cargo capacity for a 26 foot trailer. I'd expect you're over the limit even before adding any water, propane, or a single item of clothing.

And carrying capacity is generally based on an evenly distributed load, which yours definitely is not.

Adding more tongue weight MAY reduce the sway, but maybe not. That's a huge point source on a long lever way back at the rear, so any little rocking there just gets magnified as it projects forward.

Maybe a Hensley might help?

My advice, given the amount of money you've probably already invested in this, is drive VERY SLOWLY (always UNDER the speed limit), be extremely careful with turns and sudden moves, don't drive in windy conditions, and always keep considerable distance from other vehicles.

You need to take your TT to a scale and weigh the total trailer weight and the tongue weight. Tongue weight should be at least 10% of trailer weight. If you can shift some of your cargo forward that would help. Sway control would help but I think you need to get the weight balance under control first.