Recently purchased a new Roku Express. I have a WD external HR with my bluray collection. I copied all discs with the same settings. Some will play on the Roku while others cause the Roku to freeze and re-start. File size does not seem to be the issue and when they do play, picture and sound is great. Files are .MKV and average 9GB in size. The drive is a 4 TB drive connected via usb and firmware is up to date. Appreciate any advice. Cheers