One of my devices is a Fire Stick. I don't have any issues with the channels when using it, so it is hard for me to put a finger on your issue. The Fire Stick is a low memory device, so free up as much memory/cache as you can. Also, you can look into tweaking the advanced video settings. Some people claim it performs miracles while others report little if any success. You can Google "advanced video settings kodi" to find information on the topic. Make sure your tweaks are intended for the Fire Stick and not for a device with more RAM.