A full pull to the rear of the trigger is required to make the transfer bar work properly, if you release the trigger at the break, the transfer bar may not be in position for full impact to the firing pin. If you've cleaned it well as mentioned in the Centerfire FAQ and Help sticky which is SOP for any new NEF/H&R firearm, contact H&R and make arrangements to have them fix it on their dime including shipping, contact info is in the same FAQ. Several other members have had the same problem with Sportsters, suspect is the timing/function of the transfer bar. While it's there, you might ask them to lighten the trigger if that suits you and it's a good time to order extra barrels, too!
Tim