UWP XamlParseException AccessDenied Can't find a Resource

It appears that somehow my Visual Studio instance has lost access permissions to the ThemeResources XAML file...?
In design view, I get the following error:

An Unhandled Exception has occurred
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Details:
System.UnauthorizedAccessException
Access is denied. (Exception from HRESULT:0X80070005 (E_ACCESSDENIED)

I can still build and deploy the app locally but the first time the application tries to load a ThemeResource (whether from the SDK or a Nuget package), it blows up with the following message:
Windows.UI.Xaml.Markup.XamlParseException: 'The text associated with this error code could not be found.

Cannot find a Resource with the Name/Key TextControlBorderBrush [Line: 798 Position: 44]

Initially that message referenced a resource used by the NavigationView, but I commented that control out and got this message instead.

This is a problem on my existing application on this device as well as any new blank UWP apps I create. Now, I don't control this laptop so I don't know what all has been done to it. Everything I do on the internet has to travel through my employer's VPN and they've made some changes over the last week to handle all of the new WFH traffic. I started to install VS2019 on here a week ago but "Paused" the install never got to finish. This error prompted me to finish the install in hopes that it would fix the problem, but it did not.

Any help would be greatly appreciated.