DIAGNOSIS The internal storage is nearly full or the cache is corrupted. The MediaTek MT9618 chipset can bog down.
FIX Hold the power button on the remote. Select 'Restart', not 'Power off'. Then go to Settings > Device Preferences > Storage. Clear cache for each app, especially the Google Play Store and Google TV Home. Uninstall unused apps.
IF THAT DIDN'T WORK Perform a factory reset. Settings > System > About > Factory data reset. This wipes all data and apps.
HEADS UP Do not use the 'fast startup' feature. Go to Settings > System > Power & energy and disable it. This forces a full boot and clears memory leaks.