The power factor,if it was an issue, would tend to affect the feeder overcurrent and not the loads downstream. And this would be so if the power factor suddenly got worse, because your reactive current has increased on the feeder. But from the sounds of it, there is a problem in the hydraulic system with the three motors driving it. I am assuming you had a millwright have a look at that system also. From your description none of the other banks of motors are failing, so its probably not on the distribution.
