It sounds like there's probably something wonky about the connections between the battery, the converter, and the trimetric, rather than a fault in any of those units themselves.
How are the battery, the trimetric, and the converter connected together in relation to each other? In particular, does the trimetric's current sensor actually see the current from the converter to the battery? If, for example, it uses a current shut on the ground lead of the battery, does the converter connect to the battery rather than the chassis side of the shunt?