I put GHK-Cu into HA serum too and never saw any leftover layer or stickiness.
Finished a six-week injectable run a month back and noticed clear changes, mostly in an old leg scar that looks far better now. Picked up some cosmetic-grade powder, made a 1 g in 50 mL mix with hyaluronic acid serum, and wonder if others get the same thin tacky coating once it dries. Also saw some temporary fine-line tightening a couple times. Someone suggested blending in Snap-8 for better moisture, but I am unsure if that is the right step or if the current mix is simply off.