Seem like this was caused by LiveShare.
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The ‘CascadePackage’ package did not load correctly
As for my two issues:
On one machine…the error went away by starting VisualStudio.
On another machine I went into Tools->Get Tools and Features…
Click onIndividual components
search for Live Share. Uncheck it.
Restart VS.Go back into Tools->Get Tools and Features…
Click on
Individual components
search for Live Share. Check it back.
More about the ActivityLog…
Visual Studio uses a /log
option on update. This creates the ActivityLog.xml.
More here /Log (devenv.exe) This is something you can also do yourself.
The description part of the ActivityLog.xml will list where the problems are. Here is an edited breakdown of the original message in the OP.
<entry>
<record>894</record>
<time>2021/03/05 13:52:21.259</time>
<type>Error</type>
<source>VisualStudio</source>
<description>SetSite failed for package [CascadePackage]Source: 'System.ComponentModel.Composition'
Description: The composition produced multiple composition errors, with 3 root causes.
The root causes are provided below.
Review the CompositionException.Errors property for more detailed information.


1) No exports were found that match the constraint: 
	
ContractName	Microsoft.VisualStudio.Cascade.Commands.IJoinCommandLineHandler
	
RequiredTypeIdentity	Microsoft.VisualStudio.Cascade.Commands.IJoinCommandLineHandler


Resulting in: Cannot set import '
Microsoft.VisualStudio.Cascade.CascadePackage.JoinWorkspaceCommandHandler (ContractName="
Microsoft.VisualStudio.Cascade.Commands.IJoinCommandLineHandler")' on part '
Microsoft.VisualStudio.Cascade.CascadePackage'.

Element: Microsoft.VisualStudio.Cascade.CascadePackage.JoinWorkspaceCommandHandler (ContractName="
Microsoft.VisualStudio.Cascade.Commands.IJoinCommandLineHandler") -->
Microsoft.VisualStudio.Cascade.CascadePackage


2) No exports were found that match the constraint: 
	
ContractName	Microsoft.VisualStudio.Cascade.Commands.IShareCommandLineHandler
	
RequiredTypeIdentity	
Microsoft.VisualStudio.Cascade.Commands.IShareCommandLineHandler


Resulting in: Cannot set import '
Microsoft.VisualStudio.Cascade.CascadePackage.ShareWorkspaceCommandHandler (ContractName="
Microsoft.VisualStudio.Cascade.Commands.IShareCommandLineHandler")' on part '
Microsoft.VisualStudio.Cascade.CascadePackage'.

Element: Microsoft.VisualStudio.Cascade.CascadePackage.ShareWorkspaceCommandHandler (ContractName="
Microsoft.VisualStudio.Cascade.Commands.IShareCommandLineHandler") -->
Microsoft.VisualStudio.Cascade.CascadePackage


3) No exports were found that match the constraint: 
	ContractName	
Microsoft.VisualStudio.Cascade.Contracts.IVsCascadeClientService
	RequiredTypeIdentity	
Microsoft.VisualStudio.Cascade.Contracts.IVsCascadeClientService


Resulting in: Cannot set import '
Microsoft.VisualStudio.Cascade.CascadePackage.ClientService (ContractName="
Microsoft.VisualStudio.Cascade.Contracts.IVsCascadeClientService")' on part '
Microsoft.VisualStudio.Cascade.CascadePackage'.

Element: Microsoft.VisualStudio.Cascade.CascadePackage.ClientService (ContractName="
Microsoft.VisualStudio.Cascade.Contracts.IVsCascadeClientService") -->
Microsoft.VisualStudio.Cascade.CascadePackage


</description>
<guid>{D86E17D6-7FC7-47F4-9259-21748EDFF93B}</guid>
<hr>80131500</hr>
<errorinfo></errorinfo>
</entry>