This is extremely unusual as ther HW100 has the reputation of being the least pellet fussy of all the modern rifles. MIne is happy with Falcon Accuracy, Bisley Mags, AA Field, H & N Trophy and I know Zini has used FX.
After doing what Davy suggests re cleaning and checking scope fittings etc, check the allen bolts holding the stock to the action. Then I suggest you try shooting it without the silencer, as the pellets may be clipping on the way out.
Do all of these things one at a time, so you know what you've eliminated.
Suggest you try all of the above with the H&N as the