Assuming I have understood the question, can I ask how you are measuring the power consumption ?
In the UK for 400kVA we would expect metering by current transformers and voltage detection all in units that belong to the supplier so the billing is for watts (true power) anyway, not kVA (which is only the same as true power when the load is resistive and zero power factor).

To verify if the power factor correction caps are doing their jobs you need to be able to measure the current into them, into the load, and from the supply, as well as the power factor (so a voltage and current measurement) on the supply side.

If the capacitor values are known then the expected current in them can be calculated in the usual way from Z=1/(2.pi.F.C).

IT is possible if the current is lower than this predicts that one or more caps in the bank is open circuit.

If the capacitors are electrically leaking they will run hot.

But the far harder question is if the cap value is correct for the loads you have - and for that you need to measure power factor. At a few hundred amps per phase, I'd expect a power factor meter that uses clamp on current transformers and a voltage probe will be needed. Such things can be hired in if not part of the permanent equipment on-site.

Mike.