mp4 export stops playing

hey everyone, i just exported a 1.5 hour video with only a source video file and some text/legacy titles in them and it seems that upon playback, the video stops halfway. the video plays until that halfway point, time stamps still run and the video length is as long as it needs to be, but it stops at one frame and is pretty much just a picture. no audio, no movement, nothing.

export and encoding took about 1.5 hours on a macbook air 2015, macos high sierra, premiere pro cc 2017, 8 gb ram, about 16 gb left in storage. these are my export settings too: