I do not believe either pump is VFD or soft start rated, this could be cause of winding failures. Yes under voltage can cause problems, but you state amps and volts were all good. Is pump controlled by contactor? Is there a coil that drops out when shut off? Could wiring be wrong? Single phasing cause loss of power and vibration. Verify contactor contacts are in good shape.
Pipes typically do not break without excitation. Impeller out of balance, pump not fully submerged, hydraulics not happy, single phasing....did you check for proper rotation?
Sorry still confused on your piping arrangement. You state broken pipe but you also state "up from the pump through the hose"? IF the "hose" has a hole in it, you no longer have 10' of TDH.