C dose overshoots and, when combined with A+B, is too large for the mix chamber capacity.
Repair the valve (see valve manual 312782).
Tighten or replace valve.
Check for pressure pulsations:
See E-3: RATIO HIGH ALARM and E-4: RATIO LOW ALARM.
It may be necessary to restrict the flow rate through the component B or C dose valve by adjusting its hex nut. See manual.