If you experience an issue with loading highlights or if your overlay doesn't work occasionally, please make sure that you have set DX11 as your default DirectX in League of Legends, and that Highlights are turned on.
You can read more information about DX11 in League from Riot Games article here: https://www.leagueoflegends.com/en-us/news/game-updates/help-us-beta-test-dx11-support-for-league/
How to set DX11 as the default one?
Simply go to C:\ Riot Games > League of Legends > Configs > game.cfg and open it with a notepad.
You’ll need to add the DX11BetaTest=1 line to your [General] configs. And also make sure that you have PreferDX9LegacyMode=0
After adding them, restart your client and try again!
If the issue would still persists, please contact us and we will do our best to assist you!