MSIX App Attach - VHDX doesn't get mounted to hosts

I'm having a problem getting MSIX App Attach working and hoping someone will have some advice. I have set up an Azure Virtual Desktop host pool with 4 hosts. I have fslogix profiles working perfectly with it. I have moved on to trying to set up MSIX App Attach. I think I am 99% there but something isn't working.

I have built my packages, created the vhdx images, stored them on a share with RBAC and NTFS permissions for the users and hosts. I can upload the image to the host pool and it looks like it is working, no errors, and I can add the application to an app group. Everything looks good except that the vhdx never attaches to the hosts and therefore the app never shows up for the user.

I confirmed I can browse to the azure file share from the host without issue. And I have copied the vhdx to the host and can attach it manually to the host. I cannot manually attach the vhdx directly from the azure file share. It says I don't have permission despite the NTFS and RBAC permissions showing that my AVD Users AD Group and my AVD Hosts AD Group have the appropriate permissions. Permissions also seem fine since the MSIX packages upload to the host pool and all tests pass and I can see the applications in the package. I have tried everything and am at a loss. I am in a GCC High tenant. Is there some security setting/restriction in GCC High that would prevent App Attach from mounting the VHDX from the Azure file share? The fslogix profiles attach to the hosts and work fine. Any help or suggestions would be greatly appreciated.