In task manager, you might see Credential Guard & Key Guard using high CPU. If you inspect the details, you will find that the process name is LsaIso.exe. 

 

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A possible cause can be Citrix Offline Plugin. This is a legacy application that is not removed when Receiver or Workspace app is removed. 

If Citrix Offline Plugin is installed on the computer, uninstall this and reboot to verify that this is the cause of the high CPU for Credential Guard & Key Guard. 

If the CPU is still high for Credential Guard & Key Guard, follow the steps in this Microsoft article to identify other applications or drivers might have loaded into this process.   https://docs.microsoft.com/en-us/troubleshoot/windows-client/performance/lsaiso-process-high-cpu-usage 

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Problem Cause

In Windows, the LsaIso.exe process runs as an Isolated User Mode (IUM) process in a new security environment that is known as Virtual Secure Mode (VSM).  Applications and drivers that try to load a DLL into an IUM process, inject a thread, or deliver a user-mode APC may destabilize the entire system. This destabilization can include the high LSAISO CPU scenario.
See here in this sample memory dump, ctxpidmn is loaded in the thread:

When troubleshooting performance issues, review all the programs installed and check for legacy or unsupported products that might be causing your issue.