This is somewhat relevant to this thread. Because the original ZO, which it appears this boat has, will need to either have the firmware on the original Garmin pucks updated, or be upgraded to the latest single puck ZO.
The original ZO, with the puck firmware supplied by ZO, sort of works, but doesn't work correctly at this point. That's because the GPS 18x pucks have a bug related to the GPS Week Number rollover that happened on April 6, 2019.
GPS Week Rollover
Garmin GPS 18x Firmware Issues and Updates
The bugs caused accuracy issue with the GPS data. And the accuracy varies based on which and how many satellites are in view at any point in time.
This manifests in Zero off behavior that ranges from just being somewhat out of whack to totally not working and surging badly based on the the position of the GPS satellites in the sky. I've also seen cases where the ZO diag screen reports one of the pucks is not working because of the bug.
Unfortunately, updating the puck firmware isn't a simple process. ZO doesn't provide a built-in firmware update procedure for the pucks. Additionally, it's a two part process. The actual puck firmware must be updated, which completely resets the configuration of the puck. Then the puck must be re-configured precisely as ZO expects. Otherwise, ZO won't recognize the puck.
I built the required cables, figured out the configuration of the pucks that ZO expects, and have updated our club boat. I've also heard that Perfect Pass was doing the updates for folks at one point. ZO's official "fix" is to upgrade to the new single puck GPS system.