I wonder if this has to do with all the fake micro sd cards being sold out there. Even Amazon was hit by a rash of fake cards. A samsung rep was actually posting on Amazon about their cards. If it says it was made in Taiwan on the packaging, it's fake. The fakes are so good, they fool the phone and even computer software into thinking the cards are actually, 32 gb, 64 gb, etc, when actually all they are is 8 GB at most. So your phone writes to it thinking the capacity is what is listed, then files start getting corrupt, videos start messing up, etc.