Those of you having trouble, try rebooting while holding the shift key. That starts in safe mode, which stops all third party launch items from running. If that fixes the problem, that tells you to start looking at those launch items for the culprit.
support.apple.com
You can find launch items in the Login items section of System Settings, or in the folders listed below.
~/Library/LaunchAgents (~ is your users folder)
/Library/LaunchAgents
/Library/LaunchDaemons
/Library/StartupItems
/Library/Extensions
/System/Library/Extensions/
Start up your Mac in safe mode - Apple Support
To help determine whether an issue is caused by software that loads as your Mac starts up, you can start up your Mac in safe mode.
You can find launch items in the Login items section of System Settings, or in the folders listed below.
~/Library/LaunchAgents (~ is your users folder)
/Library/LaunchAgents
/Library/LaunchDaemons
/Library/StartupItems
/Library/Extensions
/System/Library/Extensions/