Do you have a current clamp meter? I would check the current consumption of the flood pump, and see if there is a difference phase to phase as well. And not out of the coolant. The coolant will reduce the RPM and thus the counter EMF which raises the current draw. It might be at the edge of what is acceptable. How "rich" is your coolant?
The motor overload is wired into the Emergency stop circuit which is why the whole machine stops.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)