I have realized my mistake and was under the assumption min, max annotations were part of the data in coco… when instead it is required I calculate that myself in my data loader
        # get bounding box coordinates for each mask
        num_targets = len(targets)
        boxes = []
        for i in range(num_targets):
            box = targets[i]["bbox"]
            xmin = box[0]
            xmax = box[0] + box[2]
            ymin = box[1]
            ymax = box[1] + box[3]
            boxes.append([xmin, ymin, xmax, ymax])