IGBT-based capacitor charge transfer and thyristor-based capacitor discharge
Are you using GroundPlanes? At 5 MHz frequency content (100 ns edges), the copper foil begins BEGINS to provide some magnetic shielding.

One square of copper foil, default thickness of 35 micron (1.4 mils) of weight 1 ounce/foor^2 has resistance of 1/2,000th ohm. A current of 1,000Amps thru that one square produces 0.5 volts. And 3 squares of such foil, any size squares, produces 1.5 volts upset, adequate to invalidate many a "logic" control signal for your high-current devices.

Draw the Grounding, the RETURNS,  using a quadrille path (lots of squares), to scale. Count the squares, understanding each is 0.0005 ohms.