Content of second tab (in tabpane) is not rendered till after resize of app

A loop creates multiple (ic 2) tabs in a tabpane.
Each tab is identical as each is a load of the same file.fxml;
The first tab is in focus and displays content, the second displays (the identical) content (btw the controller will eventually data) only after the app is resized. (btw the controller will add data)

for (short i = location.getNs2b(); i > 0; i--) {
                this.getTabs().add(makeTab(location,i));
            }

private Tab makeTab(Location location, short i) {
        Tab tab = null;
        try {
            FXMLLoader loader = new FXMLLoader(ManageLocation.class.getResource("Subset.fxml"));
            tab = (Tab) loader.load();
           .....