Skin settings no longer available after migration from Kodi 15

Hi all,

I'm trying to fix my Kodi 15 skin to make it work with Kodi 17.
An issue I'm having is that I have a 'resources' folder with 'settings.xml' which somehow is no longer 'seen' on Kodi 17.
(Selecting my skin in the addon section displays no 'settings' button any longer.)

Somehow I assume that it is not allowed to use these settings.xml for skin settings. (I see this construction being used with all other types of addons.)

I used strings.xml which I replaces with .po files, but that does not change the effect.
Also I used to have a shortcut; "Addon.OpenSettings(skin.my_skin)" which now stalls...

Does anyone know if there are any changed requirements here?

Thanks!
Jeroen