You wouldn't have any VFDs bouncing back harmonic echoes?
While there are various ways...
One VFD scheme uses a 'low pass filter' to establish a 'DC tank' -- in the form of a very hefty capacitor, or two... which is then drained by IGBTs to craft AC wave forms by stacking DC transient impedances.
If these massive capacitors cause enough phase shift then the indicator lights would read 'dead.'
A scope or strobe set up would discover if these transitory outages are synch'd to 60Hz or some harmonic. ( 120 Hz = low pass ripple frequency )