have you ever tried to repair or reinstall SW and the add-in removes old versions while saving the settings; because if you have reinstalled the 2016 versions on the 2015 it can create conflicts.
@remrem: FYI, in 2016 version, the settings are in:
C:\Users\nom_utilisateur\AppData\Local\Visiativ
When launching a tool in 2016 version, it checks if the options exist in the 2015 version (i.e. in the Axemble folder) and the copies in the Visiativ folder
So in addition to your answer, you have to delete the Axemble and Visiativ folders to reset the settings.