With the suppressor (be it full length or shorty version of the SureFire SOCOM762), I have had no issues at all with cycling.
I think one other HKPro member cut his down to 13” but lividly had no issues cycling when shooting without a suppressor.
FWIW, I shoot Black Hills 175gr SMK. Recently tested out Berger ammo (168 gr, 175 gr, 185 gr) and will likely test out the Black Hills 175gr TMK. Am hoping my gun likes the Berger because it supposedly has better BC.
Getting older... need to check my notes...