Measure the voltage across the gnd and power pins on the nrf module for the low power and high power modules when in use. It is possible the hi power one is drawing more current and if the regulator cannot supply it then the voltage will likely drop below the minimum required.
Since it is the same chip and sofrware there should be no noticable difference, so you need to become the investigator and look at voltages, connections etc to see if you can locate the problem.