CANopen addressing scheme?
CANopen isn't "plug &amp; play". The identifiers - CANopen calls them COBID - that you mention are indeed as per the standard (DS-401 etc) but they are just the default settings. Factory settings if you will. For each TPDO/RPDO pair, you need to configure the COBID so that sender and receiver are looking for the same ID. You might also potentially have to configure size (DLC), PDO mapping and PDO communication parameters.

The reason why you see some strange COBID on the bus is likely because someone has already done the above configuration. This is done by SDO access to the Object Dictionary and can either be done one single time from a PC or similar, followed by a write to the CANopen save object. Or it can be done at system start-up, when one node sends out various SDO messages when node to be configured is still pre-operational. In case of the latter, you should observe lots of CAN identifiers for SDO around >0x500 during start-up.

CANopen is ridiculously flexible so there's a lot of degrees of freedom here.




  This is verified by the motor controller, that will fault if the sync message goes missing like when unplugging the CAN bus. 


If there's just 2 nodes then that's not what happens. The CANopen sync message is a higher layer concept. Rather, the remaining node fails to get acknowledge bits in the low-level CAN frame set by a listening node. If this happens enough times, the node will rapidly go into error modes, eventually ending up "error passive" and completely disconnected from the bus. This is guaranteed by the CAN hardware and data link layers and has nothing to do with CANopen.