long render hangs indefinitely.... hep!

Howdy folks,

I am trying to render a 2.5 minute animation, which is estimated to take 15 hours to render, but suddenly hangs (without error, just endlessly) after 13.5 hours!  I don't know what to do, it's so frustrating.  I left the drive working overnight, awoke to see it still working with just an hour and a half remaining, and then it just stays that way without making any further progress.  I check the status of the app and it has not failed. I am able to access all of the data on the drive without a proble, (I opened AfterEffects and was able to move through that portion of the video in the timeline, albeit slowly.).  I pause Media Encoder and resume - nothing changes.  The only thing I seem to be able to do is cancel, which works fine *except I lose 13 hours of rendering!  It's a performance video and the same 4K shots (transcoded to h264) from start to finish (long takes), so I don't think it's some bit of bad footage throwing it off. Nothing new has occurred around that time, and I have been able to render the whole thing three prior times in rough format but with the same h264 compression settings.  Any ideas??