Set the order of items in StaggeredGridLayoutManager and RecyclerView

Question

I'm trying to integrate a timetable into my app. At first I used a normal GridLayout, but I want to connect school subjects. So I switched to StaggeredGridLayoutManager to set different heights to the items . Everything works, except for one thing. If a subject goes only for one lesson on a day, the first item in the next row is placed in the gap.

Here's what I mean:
This is what I expected
How it looks

Number 7 should be Monday, not Thursday.

This is in my ScheduleActivity to call my custom adapter

RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.schedule_recycler_view);
    recyclerView.setHasFixedSize(true);

    StaggeredGridLayoutManager staggeredGridLayoutManager = new StaggeredGridLayoutManager(7, StaggeredGridLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(staggeredGridLayoutManager);

    ScheduleAdapter rcAdapter = new ScheduleAdapter(subjects);
    recyclerView.setAdapter(rcAdapter);

And here is my Adapter

public class ScheduleAdapter extends RecyclerView.Adapter<ScheduleAdapter.ViewHolder> {

private ArrayList<SubjectModel> items;

// Provide a reference to the views for each data item
// Complex data items may need more than one view per item, and
// you provide access to all the views for a data item in a view holder
public static class ViewHolder extends RecyclerView.ViewHolder {
    public CardView cardView;
    public TextView content;

    public ViewHolder(View view) {
        super(view);
        cardView = (CardView) view.findViewById(R.id.schdule_card);
        content = (TextView) view.findViewById(R.id.schedule_content);
    }
}

// Provide a suitable constructor (depends on the kind of dataset)
public ScheduleAdapter(ArrayList<SubjectModel> items) {
    this.items = items;
}

// Create new views (invoked by the layout manager)
@Override
public ScheduleAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    // create a new view
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.schedule_card, parent, false);
    return new ViewHolder(view);
}

public static float convertDpToPixel(float dp){
    DisplayMetrics metrics = Resources.getSystem().getDisplayMetrics();
    float px = dp * (metrics.densityDpi / 160f);
    return Math.round(px);
}

// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
    // - get element from your dataset at this position
    // - replace the contents of the view with that element
    final SubjectModel subject = items.get(position);
    int lessons = subject.getLessonCount();

    int i = lessons*2-2;
    int height = (int) (holder.itemView.getMinimumHeight()*lessons + convertDpToPixel(i));
    holder.cardView.setMinimumHeight(height);

    String text = subject.getSubjectName().substring(0, 2)+"\n"+subject.getSubjectRoom();
    holder.content.setText(text);
}

// Return the size of your dataset (invoked by the layout manager)
@Override
public int getItemCount() {
    return items.size();
}

}

Sry that the pictures are only linked. I am new here and still have no authorization to integrate the pictures directly.

Does anyone have an idea how I could solve the problem? I couldn't find anything yet.

Thanks for your help!