The single trigger Huglus have what I believe is called a drop sear arrgt. Part of the trigger assy is called the selector. It engages the sear blocks for either the upper or lower barrel. In turn, the sear blocks engage the hammers. So, to operate correctly, the sears on the selector and the sear block need to work in concert. On my second trigger pull for the top barrel, a radius on the leading edge of the selector sear prevents the selector from catching the sear block and releasing the hammer. When you pull the trigger there is no resistance.
In contrast, the leading edge on the selector for the bottom barrel is sharp, and catches the sear block reliably. Whether the radius was an attempt to refine the trigger pull, or developed through wear is a mystery to me. I shoot the bottom barrel 90% of the time, so the affected barrel has probably seen less than a box of shells. I should point out that Prophet River has responded favorably in dealing with a warranty fix.
Memaquay - due to the nature of the design, this problem will only occur on the second shot for the affected barrel. If you reverse the firing sequence, ie affected barrel on first pull, the gun functions reliably. In my case, I suppose I could use it as single, non-selective trigger gun, but I thats not what I paid for. Suggest you look into matters a bit further.