Evergreen88 I had the same issue of the grouphead not warming up with my ECM Classika. It went away by itself after a few days of usage.
Often when a machine is new, there is some trapped air that needs to work through, expansion valves need to work for a bit to shape themselves to the seat etc. So it’s not unusual to find this. Ultimately though a design needs to make a themosyphon stall very difficult to happen or even induce.
e.g. if you lift the lever for 10s with the machine hot but switched off at night, you will pretty much guarantee a thermosyphon stall the next morning. A machine can, and should, be designed to partially/completely resist this.
It will all come good though….I wouldn’t worry about it..