This often happens with many machines as users "get used to them".
Your machine, like most will drop to approx. 0.5Bar during a 600ml milk texture event and should recover promptly once your done.
The tip of the Diadema has 2 narrow 0.8mm holes. Older models had more like 1-1.2mm and as this is the source of restriction, I think you could safely drill the tip out a little if you choose to.