Same here on VS2019 16.4.3. Upgraded the extension from 2.10.8.8121 to 2.10.8.8132 (latest as of this writing), immediately started getting two of these errors as soon as I loaded a folder cloned from a Github repo. First one says that PullRequestStatusBarPackage did not load correctly, second one that GitHubPackage didn't. GitHub functionality is of course totally unavailable with the plugin having failed to load.

Reverting to 2.10.8.8121 instantly fixed the problem.

This might be a regression? It seems to be the same problem as described on #1810 and #1625.

Error descriptions from ActivityLog.xml:

SetSite failed for package [PullRequestStatusBarPackage]
Source: 'System.ComponentModel.Composition' 
Description: No exports were found that match the constraint: 
ContractName: GitHub.InlineReviews.Services.PullRequestStatusBarManager
RequiredTypeIdentity: GitHub.InlineReviews.Services.PullRequestStatusBarManager 
...
SetSite failed for package [GitHubPackage]
Source: 'System.ComponentModel.Composition' 
Description: No exports were found that match the constraint: 
ContractName: GitHub.Commands.IBlameLinkCommand
RequiredTypeIdentity: GitHub.Commands.IBlameLinkCommand 

Same here on VS2019 16.4.3. Upgraded the extension from 2.10.8.8121 to 2.10.8.8132 (latest as of this writing), immediately started getting two of these errors as soon as I loaded a folder cloned from a Github repo. First one says that PullRequestStatusBarPackage did not load correctly, second one that GitHubPackage didn't. GitHub functionality is of course totally unavailable with the plugin having failed to load.

Reverting to 2.10.8.8121 instantly fixed the problem.

This might be a regression? It seems to be the same problem as described on #1810 and #1625.

Error descriptions from ActivityLog.xml:

SetSite failed for package [PullRequestStatusBarPackage]
Source: 'System.ComponentModel.Composition' 
Description: No exports were found that match the constraint: 
ContractName: GitHub.InlineReviews.Services.PullRequestStatusBarManager
RequiredTypeIdentity: GitHub.InlineReviews.Services.PullRequestStatusBarManager 
...
SetSite failed for package [GitHubPackage]
Source: 'System.ComponentModel.Composition' 
Description: No exports were found that match the constraint: 
ContractName: GitHub.Commands.IBlameLinkCommand
RequiredTypeIdentity: GitHub.Commands.IBlameLinkCommand 

I’m experiencing exactly the same problem. We have even identical versions.
Only difference is that on reverting to version 2.10.8.8121 of the GitHub extension the problem didn’t go away.
P.S,
Workaround fix, which worked for me:
Close VS. Delete files in ComponentModelCache folder. They will be recreated when VS starts.
%localappdata%\Microsoft\VisualStudio\16_xxxx
e.g.
%localappdata%\Microsoft\VisualStudio\16.0_574bb467\ComponentModelCache

I've had the same problem, but instead of reverting versions, I tried @MakCom's suggestion of clearing the ComponentModelCache - this worked for me with the latest version.