One CAN channel each route.
All works perfect except for Listen-Only mode which behaves strange (?)
If one and only one of the CAN channels is setup with Listen-Only, both UDP ports receive correct datagrams, it doesn't matter which of the CAN channels have enabled Listen-Only as long as only one of the two channels is setup with Listen-Only.
If I enable Listen-Only on both CAN channels, no UDP datagrams are sent at all.
have you connected both CAN channels to the same CAN network? How many other CAN nodes are connected to it? Any other that acknowledges your CAN messages if both gateway channels are in listen only mode?