Upon reflection I can explain the problem with the truss with the deflected straining beam - the original structure had no belfry. When it was rebuilt, a belfry was added and the gallery was reduced from three sides to one. We believe that some of the timbers that had been used in the gallery framing were re-purposed to construct the belfry, including a large pine timber that was cut to form two 'sleepers' that run from the end wall plate to the first truss and support most of its weight... with the logical consequence that that truss is significantly overburdened.