I’d serve the sauce on the side too, the thigh is so moist that the skin crisps upbut there is enough residual moisture in th meat that when you put the lousy sauce on the top of the skin, you end up having the “outgassing moisture” from the meat coming from the inside and the sauce moistening the top resulting in in the skin getting soft again.
If you think the sauced skin is critical to the end product, finish it off with some direct heat to brown off the sugars in the sauce and that should help but, watch it, the sugar can burn faster than you might expect.
Corey, don’t be surprised if this thread gets moved, I think Chris might put this under “recipes”.