1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.
2 - Does the issue present in this mode ?
3 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.
4 - If not - there could be something in the main User Account playing up. To further isolate this - Set up users, guests, and groups on Mac. Then log out of the Main User account and log into the dummy account and test again if the issue persists.
5 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.
6 - If after performing each of the above steps is the order that have been presents and still have issues - please advise for possible further assistance.
Any Third Party Applications that will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and comprising the Operating System
Any of the below should be removed as per Developers Instructions
This will include CleanMyMac , This will include BitDefender ,
This will included Norton Antivirus , Sophos Av Software
Intego AntiVirus, McAfee, MacKeeper, Avast AntiVirus
Ad Guard, Webroot , ESET
The The Built in Security is all that is required.