I have recently upgraded to LR6. I spent some creating a slide show from over 100 raw Lumix GH3 files. It played OK in the program but, when I exported the Slide show to MP4, the Mp4 only played 20 or so shots before reverting to sound only. Also a couple of the shots that did appear were in very low res. Before this I had a couple of problems where shots were suddenly labelled with an exclamation mark and a message that lightroom could no longer edit them, I believe I excluded these from the slide show. Any ideas as to the likely cause?