XAML parser resolving URIs (I get odd control behavior, and "The component 'XXX' does not have a resource identified by the URI" errors.

I am currently struggling with what I assume is this issue. I have a .NET 5.0 WPF plugin architecture and encounter errors if I have multiple plugins in different assembly load contexts. It seems to come down to issues with the XAML parser resolving URIs (I get odd control behavior, and "The component 'XXX' does not have a resource identified by the URI" errors.

Given that this is still an open issue, is there any known way to work around the problem? Thanks.

_Originally posted by @mikeoliphant in https://github.com/dotnet/wpf/issues/1700#issuecomment-776875639_