I need some more information to get a clear picture.
1. Is this a WordPress multisite?
2. When are you seeing the CPU hike?
3. Is it a CPU spike or constant usage?
4. Your screenshot says mysql uses most CPU. Can you verify the process?
5. Do you have any caching enabled(object or DB)?
6. Can you try with all plugins deactivated except the WPFront User Role Editor?