Premiere Pro - ran out of space while "Muxing" and now I want to finish the job

Hi there

I exported a sequence from Premiere and it took about 18 hours to render (4k video :-s).  It created a .m4v file and an .aac file and then started to 'mux' them together. The problem is that the m4v is over 19Gb and the mux created a tmp file of 19Gb and then required ANOTHER 19Gb to produce the final file... I hadn't anticipated that I would need that much room on my 256Gb MacBook Pro.

Premiere pro didn't warn me that there wasn't room, it was Mac OS that notified me. I cleared the space but Premiere did not continue to Mux... it just hung and didn't finish the job. I left it for a long time to confirm it wasn't going to finish the job and had to quit it.  Now I have the rendered m4v and aac files and I would like to have those files combined into one mp4.

The problem is that there doesn't seem to be any Adobe solution, in Premiere, Media Encoder or After Effects, to process them. I can't import then and reexport them.  I researched and downloaded tools (mp4tools and Hybrid) to Mux them with passthrough options - the MP4tools DID easily and quickly combine them but the result was wrong... instead of the frames being ordered like 1 2 3 4 5 6 7 8 etc, it combined them like 1 2 - 5 6 - 3 4 - 7 8, producing very jittery video. I suspect it's how the multiplexing worked in that software.

I would rather not have to re-render 18 hours again. Is there any way I can resolve this without resorting to the re-render?