Text frames disappearing after applying a ParagraphStyle

I don't have a lot of Indesign experience to say the least but I was asked to investigate if it was possible (using indesign server of scripting) to start a new document, apply a master spread page, insert some paragraphs and applying some paragraph styles.

The solution I came up is this

// define template
var indesignTemplate = new File("/e/boek_NL.indt");
// open the template
var doc = app.open(indesignTemplate);
// get master page
var masterPage = doc.masterSpreads.item("A-Master");
// get first page
var page = doc.pages.item(0);
// apply master page to our first page
page.appliedMaster = masterPage
// get paragraph style
var paragraphStyle = doc.paragraphStyles.item("_2.ondertitel_bladzijde");
for (var i = 0; i < masterPage.textFrames.length; i++) {
     var textframe = masterPage.textFrames.item(i);
    if (textframe.label === "flow") {
        for (var x = 0; x < 5; x++) {
            // insert another new paragraph
            textframe.parentStory.insertionPoints.item(-1).contents = "text \r\r";
        }
       for (var x = 0; x < textframe.paragraphs.length; x++) {
         textframe.paragraphs.item(0).applyParagraphStyle(paragraphStyle);
       }
     }
}
//Save the document (fill in a valid file path).
doc.save(new File("/c/boek_nl.indd"));
// Save the document as an PDF
doc.exportFile(ExportFormat.pdfType, new File("/c/boek_nl.pdf"));
// close the document.
app.documents.item(0).close();

This works and can see my text when I comment out the applyParagraphStyle code.

From the moment that I try to apply a paragraphStyle the text gets hidden, that in the generated PDF as the INDD file. When I then open the saved indd file in Indesign and command+shift click in the empty text frame, the text appears and I also see an extra layer appearing.

I also tried applying CharacterStyles in more or less the same way but that doesn't give any problems.

I assume that the problem lays in the fact that I'm may approaching this in the wrong way ?