It's possible that your issue is caused by having multiple prefs.prop files, which sometimes happens for unknown reasons.
There should be only one prefs.prop, and that's in the savegame folder:
~/Library/Application Support/Telltale Games/TheWalkingDead/
Please check if there are additional prefs.prop files in the install folder or its subfolders.
If so, make a backup copy of the prefs.prop and delete it from the install folder.
If that doesn't help, make a backup copy of the savegame folder's prefs.prop, and then try copying the install folder prefs.prop to the savegame folder.
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