If you try these information so i hope your problem is solved
Some of these include installing the third-party apps. Third-party video apps include apps such as VLC which are available for Android and are compatible with Kindle. Just sideload them on the Kindle and you are good to go. If you have VLC installed on any other device, use Manage Kindle Devices and transfer the app to the device which you are using now. This would solve the video problem easily since these apps have a different codec of their own. If you still want to play using the original app, try hard resetting the device and hence the issues will be resolved but all the data will be wiped so it is not preferred.