Refrigerant flowrate problem in liquid line (fluctuations)

[RANGER1]

Mrr,
You mention delta P of 9.5 bar, but also 7 bar discharge pressure?
15 deg C of subcooling is very high for air cooled condenser, so condenser must be banked up with liquid (overcharged).
Can you look at raw data from stepper motor, as expect it must be modulating.
With 15 deg of subcooling & a suction/ discharge pressure currently unknown, but low delta P, TX valve selection could be at its lowest end to control correctly.
Remove some refrigerant to see effect, would expect improvement.
Check TX valve capacity at minimum load, is it really correct size.
When designing a system, normally select a condition to run & try to maintain that condition for optimum performance.
Stepper motor TX valve have very good turn down, but with high subcooling, might be on the edge. subcooling