It sounds like the code is doing exactly what you told it to; placing the label at a specific position in pixels. In the default desktop window this happens to be the bottom left, but on another device (or after resizing the window) it could be anywhere, depending on the resolution of the display.
You should instead use layouts, so that everything is set proportionally and will adjust to different screen shapes. For instance, you could use an AnchorLayout to place the label in the bottom right.