I have 362 movies on a portable USB drive (WD Ultra, 3TB, exFAT). It's about 2TB of movie files with files sizes ranging from 1GB to 9GB. The movies are in all formats (mp4, mkv, etc.), and they all play perfectly fine through the USB ports on my Samsung TV. As I digitize my DVD/BluRay collection, I add the new files to the drive. No problems until recently. Suddenly, new files added to the drive will not play ("Unsupported format"). The same files will play from a flash drive and from a powered external HDD (also exFAT). Ran chkdsk on the WD drive: all good. Reformatted the WD drive, still using exFAT for the big movie files. Reloaded all of the movies onto the WD drive, plugged it into the TV, and all movies now play...even the ones that would not play before. Today, I added three more movie files to the WD and plugged it into the TV to check. On these newly added files, I got the same error message as before: "Unsupported format." I am only getting the error message on the three newest files. Again, the other recently added movies that, previously, would not play will now play after the re-format. Any new files that I add will not play. Any clues?