I don’t use a Mac, but it might be worth asking your question here:

https://forums.garmin.com/forumdisplay.php?f=179

Also, if you are downloading from http://garmin.openstreetmap.nl/ you realize that the Family ID’s and map names are re-used so it is possible that BC is only seeing the oldest. I’d suggest deleting or uninstalling, but I don’t know how that works on a Mac.

You also might try downloading a Mac map from another site like GPSfiledepot.com and see if it loads. It won’t have the map name re-use issues that http://garmin.openstreetmap.nl/ has because the maps aren’t generated from a script.