We have been experiencing an issue that has been happening specifically on some of our CMS12 Integration environments since early this week, more specifically any reference to @Model.Current page has been outputting just the fully qualified name with _DynamicProxy appended, see example below:

It has taken a while but Optimizely support have finally found that the issue is being caused by an upgrade of the .Net Runtime from 7.0.2 to 7.0.3 - all of the environments affected (other customers are starting to experience the same issue as well now) are running Azure App Service P1v3 and it is these V3 instances that have the new runtime.

I was unable to replicate this locally until this morning. A new version of Visual Studio 2022 has been released (version 17.5.0) and since upgrading I can now replicate the issue locally, as it looks like this upgrade also updates the .Net Runtime version to 7.0.3

I believe Optimizely will be making an announcement shortly but wanted to make people aware of this issue as I am sure it will start to affect more and more people, especially with the new version of Visual Studio being released. 

A possible workaround (although hasn't worked for me) was provided by Opti support as follows:

• Add tag helper to the Razor view:
  @addTagHelper *, xxxx.Web (replace with your actual assembly name)
• Review the configs and declarations at the ViewImports file if exists
• Review the assembly, for example, moving models and views into an unified DLL assembly

I have added the @addTagHelper where necessary but the issue still persists.