So after some tests I found out that in some channels (like E!) after some minutes the video will freeze and the audio will keep going and if you stop the stream Kodi will crash, for some reason this only happen on the Fire TV 2, the Fire TV 1 is not affected with this problem.

To fix this you only need to go to Settings / Video / Acceleration and turn off "MediaCodec" and thats it.

Hope this help you.

Cheers!