Rendering to MOV Only creates 1/3 of the file

Enhancing some old movies, I have completed six or seven of them and they turned out well, All the same mp4 1920x1080. I’m up scaling them two times to 3840 x 2160 30 fps. Using the iris AI model. Outputting Codec, H265 > .MOV
One particular file so far takes the full length of time to export only to find that it only gave me a third of the file 2/3 are black blank. The source video has no issues?
I’m hoping someone may be able to give me some insight as to what the problem might be.
Thanks