Are you rendering using Media Encoder? Is your source file h264, or are you rendering to h264? Try rendering to ProRes, then transcode that file to h264.
If you need to get it out right away, try NOT sending it to ME. In export settings, instead of hitting Queue, make sure your settings are set and hit Export. See if that gets through the render. You won’t be able to do anything else in PPro while it renders.
Good Luck!
TC