All coil springs take a “set” . This is more common to see in springers but does appear in PCP’s that use springs for the hammer. Regulator creep I’ll also require more hammer spring tension to open the valve if the pressure climbs too high. That’s where I’d be looking. If you need a replacement spring because it is weak , McMaster Carr has a good selection , just need to measure coil OD, wire diameter and number of coils , I typically use a stiffer than stock spring to eliminate any hammer bounce.