I cannot tell you why it is freezing. Especially not without having all the same source materials to recreate the scenario. Even that should not make a difference.
We just provide the export plugin and Premiere provides us the rendered frame. Whether it is 1min or 10h - for us that makes no difference.
The fact that you say it renders fine from the middle to the end without problems makes it even more mysterious.
To test this I just rendered an eight hour long timeline in UHD H.264 and this completed in 1h20min on my laptop with GTX1050. No crash, no freeze.