I think the issue is here could be with styling. You have pretty complex UI with nested Grid's. On top of that you are using ImageButton. Try to add BackgroundColor to image buttons. This will reveal the actual position of image button in the view. There is chance that Image of image button can be arranged improperly in the view.

You can also check setting the ImageButton's Source normally and still the issue persists or not ...Source="image.png"