Tap the recently used appa button and close all apps.
Open Device Care and if it's not showing 100% Execellent tap the Optomize Now Button highlighted in bright blue.
If it's showing 60% Fair and the Optomize Now Button is not highlighted in bright blue there may be an issue with device care.
If so open Settings/Apps/device care and tap on storage. Clear the cache. If that does not work follow the same path and clear the data.