Hi,
Based on the instruction, the .h5 is converted to the .uff rather than .pb.
Are you using this tool for the conversion?
python3 mrcnn_to_trt_single.py -w /path/to/data/mask_rcnn_coco.h5 -o /path/to/data/mrcnn_nchw.uff -p ./config.py
More detail of MaskRCNN setting can be found in this topic:
Thanks.