The tread is already a bit old so I hope the problem is already found but anyway I still like to give some suggestion on INOEX for others.
We also have INOEX gravimetric equipment on our machines. ( IGS )
We found out the in general it's very reliabale except for one thing.
--The weighing hopper MUST be free hanging--
Sometimes after cleaning the system, the operators do not return the hopper correctly on the hooks. This results in all kinds of wierd behaviour. Sometimes the system still works but the measurement and the control are simple no longer correct.
INOEX fully controls the extruder, so bad measurement results in bad extruder behaviour.
Also be very carefull with the dust rings which are supplied by INOEX. Im my opinion they are bad. For someone with just 10 fingers it's impossibe to install them well.
Be aware that these rings do not block the hopper in anyway resulting in the same as stated above.
Coming back to the dicussion above. If the DC drive would cause a problem the INOEX will notice this ( it measures the screw speed directly ) and will try to correct it by adjusting the drive setpoint.
I suspect problem is with the cable from melt pressure sensor to plc or amplifire. Is the cable shielded? Is shield connected properly to earth? Try with new shielded cable by earthing cable shield properly. You may have re-route this cable if it is going with some power cables.