For what its worth, I only recently acquired the Seeed studio CAN-shield thanks to a generous forum user. I had been using an isolated version I made on a proto-shield. The first thing I did with the Seeed studio CAN-shield before I soldered on the stacking headers was remove the incorrect 60 ohm termination resistor, that is enabled by default, off my boards. That resistor should be 120-ohms and NOT enabled by default…
I recommend you try to either disable the termination by cutting the solder-blob-jumper trace located behind the wire-terminals or remove the resistor entirely. Both have equal difficulty, one just requires a nice hot soldering iron. I do remember reading that OBD2 diagnostic devices are not supposed to have a termination so I am not exactly sure why the CAN_shield has it enabled by default or where the 60 ohm resistance came from, but that’s all I can think of right now. I would expect the RX LED to blink if the bus wires were flipped as I know that will cause nothing to come across…
Here is a picture:
