Hi Happy SEO,
Well, the robots.txt looks find here. Could you try to fetch any of the blog page/post as google in the search console and share the screenshot here?
Also, to cross check the robots.txt (which looks fine though), you have robots.txt tester in search console where you can put any blog page/post to check if bots can crawl it. Please share a screenshot of that as well.
On a separate note, the sitemap.xml link mentioned in the robots.txt (http://www.keukensduitsland.nl/sitemap.xml) is broken. Fix that as well.