Dear Cory,
Thank you very much for your CAN bus support. It absolutely helped me a lot. Brilliant!
Dear Chris,
Without your last idea I almost gave up.
I worked over one week to get the CAN communication with Cory's code finally working - there is indeed a power problem if you power up the MCP2515 module directly with the NodeMCU power.
After I connected the MCP2515 to an external 5V power supply it worked immediately (there must also be at least one CAN receiver connected to get an acknowledgement for a CAN message which is marked as successfully sent).
Thank you so much!
Alex