Ultimaker s5 under-extruding nozzle 2

[mrender 26]

My s5 has developed and under extrusion issue on No 2 core side.  The problem seems to have nothing to do with the core, tried other cores in machine, all under extrude and do not under extrude in other s5 machines.  Currently to obtain as close to similar results as possible in this machine I need to set flow to 120%, but overall quality is not good still.  The machine seems to load material fine and extrusion during this appears identical to other machines. Front fan appears to be working fine and the extruder again seems fine.  I wonder if anyone else has had a similar issue or can suggest what is causing this?

 

Thank you