[hiccup]

First step, see if the 50A still trips when you turn off the breaker in the trunk and plug in. This will narrow it down. There are straightforward ways to determine GF vs. overcurrent but they also can be dangerous if not qualified, so I will leave out those details.

My guess is you have at least 2 problems, both related to GF, not over-current. The guess is based on the limited information you're posting but more so on my experience troubleshooting these problems over the past several years as the ELCI breakers made their way into marinas. Measuring continuity between N & G (or L & G!) with a DMM would be obvious, but it doesn't have to be the case in order to have a GF problem. Sometimes the leakage only occurs at higher voltage. There are also several ways an inverter can cause GF trips without showing continuity on a DMM depending on how its wired.