Isolated Dc Dc comverter OCP triggers Output OVP on another converter with their inputs connected in parallel and common output ground
One explanation: when the motors take too much current and their power supply shuts down, there might be a back emf on the main power due to that sudden fall in current and inductive line properties. This would/could affect the electronics power supply and cause a brief over voltage on the input that finds its way to the output and causes the OVP to shut down the converter.

Bad wiring schemes, bad earths, poor regulation on the main power source can also contribute.