Sometime in mid October I started seeing no thumbnails for some videos (ts & mp4 files, not just Tv shows). Through all the years and versions of MC I've never had this problem... It's very intermittent, maybe 1 out of 10 does not have a thumbnail. On some of these the thumbnail will generate if I remote into the server, drop into standard view, and roll my mouse over the offending file. But it doesn't work for most of them. The videos play just fine, comskip processes them fine, nothing wrong with the timeline, and Reporter says 100% thumbnails built.
Currently have 5 just in the last 5 days without a thumbnail: