Welcome to the forum!
You have a white square the same size as your page behind the drawing. It's hard to notice because it's white, and because it's grouped within several nested groups.
If you hold the Ctrl key, while you click on the white area (inside the page border), that will select the white square, and then you can delete it. After that, the export should work fine.
Possibly the white square came from the other program, and you didn't realize it.