Since there seems no one to be around from the autor side… here’s a quick workaround I figured out…
Leave the ” in the title away and instead of a space use
So the above example would be
[_su_spoiler title=Sparplan&mbsp;Check]
regarding the style I’m not sure, because I don’t use it. If it doesn’t work, may it’s a good idea to drop the ” as well, for testing ??