I would wonder if this high voltage is constant. I would start with a recording voltmeter left in place for a week to determine how much voltage variation this customer has. (if any)
Also, measure the voltage at each machine before it starts, then with no load, then again under full load.
Load calculations will be necessary for every piece of equipment, and for the shop distribution layout.
Possible solutions require a lot more information than you have provided. Maybe an electrical engineer should have been required to lay out the entire building.
Is 480 volt service available?
