Videos from iPhone showing error message

Lightroom imports the video (.mov) to my computer from my iPhone, but in the catalog, they show as a grey box with the error message: LIghtroom has encountered a problem reading this video. I am using the Lightroom mobile app to transfer my iPhone camera roll to my computer.

I can navigate to where they have been imported on my computer and play them through Windows media player, so the files are intact. I have not had this issue in the past. Looking at my catalog, this problem begins around 9/21/2017. All videos prior to that show in the catalog as a thumbnail and will scrub through the video as I mouse over it and will play when clicked on. All videos after that date show the error message.

I updated to the Lightroom Classic CC 7.0.1 to see if this would remedy the problem, but it had no effect. Just to be clear, I had the problem for several weeks prior to the update.

Any ideas on what has gone wrong?

Deb c: