CAN bus goes through periods of re-sending messages continually
All of the symptoms are consistent with the USB-CAN monitor operating in listen-only mode (not participating actively on the CAN bus). Or not understanding 29-bit messages, but that is unlikely (J1939 is explicitly listed).

From page 10 in the manual (bizarrely packed into a ZIP file), Ginkgo USB-CAN Interface VTG203B User Manual v1.1:

In tab Init Device, Working Mode should be "Normal". If it is "Silent mode" (or just "Silent"?) or perhaps some of the loopback modes, it would explain what you are observing.