Having manually stepped through 500 odd photos to fix the not properly processed problem, now when I export to MP4 from slideshow, I have about 4 or 5 black frames clustered near the beginning. If I look at the individual frames in library or develop there are no black frames. I have re-processed and get exectly the same result.
I am having similar problems with an astrophotography time-lapse I took last weekend. There are several frames where the edits I had applied across the board don't seem to be there and appear as they were pre-edit. But peeking at each frame individually, I do not see anything that stands out. Every frame looks perfect. I would like to export to mp4 from slideshow, but I don't want to have to resort to exporting each frame individually and piecing it together in another piece of software.