I see the problem. In my test installation the Import/Export Add-On was not activated. So I could not see the the 3 blue export buttons!
But I have a general question: In order to save/restore ALL Customizer settings I have to export all 3 .json files and then later import all 3 .json files?
German Translation: Currently it’s mix of german and english (text and buttons!). But I think also the english text is a little bit confusing.
e.g. “Warning: Clicking this button will delete your settings set in the Customizer area”
But actually you have 3 buttons! So I would write something like “Warning: Clicking one of the 3 buttons will irrevocably reset the corresponding Customizer area settings to their default values”
e.g “You may want to export your settings before deleting them forever”. I would add “This requires the activated “Import/Export” Add-on”
Concerning my lost settings: I think the quickest way to get my lost settings back is to reconfigure them. There is a database backup but I can imagine it’s complex to restore the database entries.