Check that the pins of the new CAN lines are correctly inserted in the connectors.
Check that the pins are not damaged.
Check that the two wires are not damaged at any point.
Use a multimeter.
Most of the faults diagnosed on the Autoscan are due to a lack of communication with the IC (J285).
If these CAN line wires were installed for the BCM 7H0 on the Ibiza FR they should work on your Ibiza 6J1.