I have recently rooted my Google Nexus 7 (2012) and flashed it with Lineage OS / Android Nougat. All is fine except the thumbnails of my video files have a green, mauve (or both) tint. This applies to 99% of .mp4 files, whilst .wmv, .flv and one odd .mp4 files have no thumbnails- just the standard camera icon. This is happening irrespective of what file viewer I use. (eg the stock "Files" app or Astro) Thumbnails of jpeg pictures are ok and unaffected. Before rooting, there was no problem in Android 5.1.1. So the problem could either be associated Nougat, or the Lineage OS. I have tried the usual emptying of caches, and deleting thumbnail folders to no avail. Internet trawl hasn't helped. Can anyone here please.