Thank you, works perfectly.
One last question about Fetch as Google in Google Search Console.
It is the Dutch version: geblokkeerd means reason = blocked and Hoog means priority High.
Has this anything to do with the theme or with our customisation of it?
You don’t need to do anything. The above three link mentioned by you is WordPress default js and css file so no need to worry about it. The next two scripts is not related to theme and WordPress itself. Might be you have added bootstrap.