Nuisance Trip GFCI by Electric Motor
A 1 Hp on 115/120v line is rated at 16 amps putting a heavy load on the motor could draw 3x the amperage some GFCI's will trip for overload.  Shop vacuums rate horse power differently than true HP rated motors. A megger is needed to check for winding leakage. Most ohm meters are very low voltage where a megger is a high voltage ohm meter. With a megger you connect 1 lead to the case and 1 to the winding I usually use the 500v setting when checking 120v motors.