Have a large chilled water plant with economizer ,6MW

When economizer is turned on, compressor suction pressure increases by 20 kpa?

Anybody with any theories as to why suction pressure actually increases when economizer is turned on.

I suspect rotors not sealing very well possibly due to wear, as well as liquid injection compounding problem

Compressor is 100% loaded
NH3
Suction 400kpa 4deg C
Discharge 1250 kpa 35degC
Economizer port pressure 800kpa
Liquid injection oil cooling
Liquid line subcooling 33to23deg c = 10deg C liquid line subcooling