Here it goes - I have been having problem's downloading and viewing video's and music through my JW Library app for a couple of months now. I was thinking that the problem was the app. Whenever I would download something to my SD card, it could play right after I downloaded but if I closed the app and restarted it and tried to play a video or music, it would tell me that "video cannot play", or "content cannot be found". It's been very frustrating. Then along came Marshmallow. I was hoping perhaps the upgrade to the new operating system would somehow magically fix this problem with JWL app - but it seemed to of gotten much worse.
I decided to wipe the SD card, uninstall JWL and reinstall it. Then I redownloaded all the publications, video's and music. At first it seemed to work - the music 'took' and I can play most of the music with no problems. But any video longer than a couple of minutes gave me the same problem as before.
I remembered I had bought my SD card from an Ebay seller so I went back to their feedback page to see if anyone else who bought this particular "genuine and authentic" Samsung EVO 128GB card was having any problems. Sure enough - there were at least 6 after me and all of them said that the card wasn't working properly and they found out it was counterfeit. So at least now I know what my problem has been all along and when my new GENUINE SD card comes tomorrow, I will be spending the next two days downloading everything again and hopefully with much better results.
It's a small piece of wonderful techology, but if it's cheap, a counterfeit or not really made for the type of device you are using it for, you can run into problems. I thought I'd post this in case anyone else is having problems of a similar nature.