Occasionally Kodi will get slow or freeze (like any other computer related device, this can happen). The best way to deal with this is to clear your cache.
Click your home button. Once there one of your options is Fire TV Settings. Click that and go to Applications
Then Manage installed applications
Then pick Kodi
For each of the next steps, wait approximately 30 seconds between each step.
Force stop Kodi
Then clear the cache.
DO NOT CLEAR THE DATA – This will erase all of your add ons. $25 (plus shipping both ways) fee to reinstall them.
You will now have to re launch Kodi