I'll take a stab at the cause: Insulation damage on the conductors in the bottom conduit where they emerge through the bushing.

It looks like the bonding-bushing lugss on the other three conduits could be pressed into their respective conductors, too.

I try to "pre-bend" wires to keep them centered in, or at least not jammed against, the conduits from which they emerge.

Larry Fine
Fine Electric Co.
fineelectricco.com