In rare cases, the Mocha HitFilm plugin or other third party plugins may develop an issue and no longer be available in the HitFilm effects panel. This can be corrected by clearing the plugin cache, to reset the plugins.
Depending on your system, the plugin cache is located at one of these locations:
Library/Application Support/FXhome/HitFilm Pro/ofxPluginCache
Close HitFilm if it is running, then navigate to that folder, and move the entire contents to the trash. Empty the trash, then relaunch HitFilm, and your plugins will once again be available.