I just received one and haven't had it apart or played with it enough to find its idiosyncracies but for PCPs in general, the three most common reasons for the symptom you describe are (in no particular order)
- Hammer spring tension set too high. Meaning the hammer spring is at the margins of reaching coil bind when you draw the bolt back to cock the gun, preventing the hammer from coming back far enough to latch behind the sear. Try backing out the adjuster at the back of the receiver by a turn or two (5mm hex drive).
- Sear engagement set too slight. This item applies to guns with a fully adjustable trigger, but the Icon has only a single adjustment for pull weight so it doesn't apply here.
- Trigger group coming loose. Same effect as the previous one, but caused by the entire trigger group pulling away from the receiver. On the Icon, the trigger group is held by hooking into the tube at the front, and secured by the stock retainer nut at the rear. Based on how it hooks in, I don't give this potential cause a high probability of being the culprit, but if the hammer spring adjustment doesn't correct it, take out the 3 stock screws and lift the action out of the stock and check that the nut at the back of the trigger is holding the trigger frame securely to the tube.