It is possible, but does not make sense.
GPS message is so standard that should not be any differencies between devices. Normally you have this kind of problems with e.g. tank or temperature sensors. Some manufacturers has used proprietary messages instead of standard messages, so other manufacturer does not understant those messages. But I doubt that with GPS.
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First check from https://www.nmea.org/content/STANDARDS/nmea_2000_certified_products that both your products are certified. If they are, you could contact to dealer.
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Do you get any NMEA2000 data to Garmin?
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Do you have termination resistors on the NMEA2000 bus?
The easies way to spy network traffic is to buy e.g. Actisense NGT-1. If you like to build your own, Buy Teensy 3.2 and necessary parts or Teensy 3.2 breakout board with can (e.g. https://copperhilltech.com/teensy-3-2-with-can-bus-breakout-board/) and use my library example ActisenseListener.