Press Ctrl+Shift+A (see everything) and then Ctrl+A (select everything).
Often you’ll find you have a stray line somewhere outside the visible part of the workspace. You can also flip temporarily to ‘User Origin’ and then change the job origin to the 4 corners to make sure the green square goes where you think it should. With what you’re showing here, the bounds from selecting everything or showing the green dot should be within your page boundary by a couple mm at least. If it’s not, you have a stray bit.