Apparently v. 8.7 had an issue with GTX 23/23ES transponders. This is fixed and a new update, v. 8.71 is available. Here is the email I got from the g3xperts today:
Please use this link to download software version 8.71. This is an update to 8.70 that corrects the issue that was causing communication problems between the G3X and your GTX 23ES transponder.
https://www8.garmin.com/support/collection.jsp?product=010-01057-00
Please use this link to download software version 8.71. This is an update to 8.70 that corrects the issue that was causing communication problems between the G3X and your GTX 23ES transponder.
https://www8.garmin.com/support/collection.jsp?product=010-01057-00
