A major current leak from a phase to ground, or less commonly, from one phase to another, can cause a voltage imbalance.A 3-phase motor may continue to run even if one of the phases is completely dead, but the motor may also fail from overheating.
The solution is to find and correct phase defects immediately. If a single phase fails, the single-phase equipment on that circuit will stop. If you see this happening, recognize the implication for the 3-phase motors and stop them immediately.A reliable way to protect motors from phase imbalance is to install a phase monitor on each motor power circuit. This device will either sound an alarm or trip out the motors if a phase is lost or if the phases become seriously unbalanced. The device itself is inexpensive. Most of the cost is for the wiring.