The end of my video gets cut off every time I finalize I have a video that I have edited and saved as mp4 several times, each time the last few seconds gets cut off.  The frame freezes but I hear the sound, and the closing credits are cut off.  Same result on a 30 minute version and 15 minute edited version.
You might want to check the framerate of your video and the one of your composition and match it.

If they don't match the app will try to fill the timeline of the composition with footage that is 'shorter' in terms of frames per seconds.