Why are the pictures on my Galaxy Note 4 breaking and turning black?

[AC Question]

I've looked all over the internet trying to figure out this problem. After transferring some pics and videos off my Galaxy Note 4 to my tablet a lot of my photos turned black with an exclamation mark in the middle. After restarting my phone and unmounting and remounting my SD card, some of the pictures refreshed and became normal again. In a group of 1500 pictures, 200 are still black. Now, sometimes when I take pictures and video, 2 hours (ish) later some will turn black too. Maybe 1 in a group of 5. I've tried saving new pictures to device and sd, I've used all sorts of file managers looking for the unbroken images but I still can't figure it out. Help?