CAN Problems with MCP2515, MCP2561 and Rpi
It could be an electrical issue with one of the CAN signal leads or the grounds.  Check the continuity of those. 

Next, make sure that the RPi is running some known-good code that initializes the CAN adapter properly. The adapter has to do a lot of work for the CAN protocol. It works semi-autonomously, so if it’s not set up properly it’ll reject frames.