FileMaker Go 15.0.2
iPod touch 6th gen 10.1.1
and iPad 3rd gen 9.3.5
A layout that is smaller than the available screen size with autosizing in use and a top navigation part is sized larger than the available screen size.
Use the three buttons in the attached fmp12 file to see the issue. When the file is first opened, you should see something like the attached image (where the footer part is not visible).
Workaround is to make the layout redraw somehow, like zoom in/out, or enter find mode, then browse mode, etc. The attached image has a script that demonstrates/documents the workaround.