Can't reference newly added image resource in Visual Studio - .NET 8.0

After successfully migrating a project from .NET Framework 4.8 to .NET Core 8.0, I’ve run into a problem when trying to add a new image as a component icon. My project still has a Resources.resx file, and all the images that were migrated still work and can be referenced from the Icon method as Resources.<name>. When I added a new image via the Resources panel (Interpolate_planes_GH), it appears correctly and looks exactly the same as the other images, but I just can’t reference it. See the video below:

My issue seems identical to this one: C# component icon - #35 by PabloDuran, except there are already resources in the Resources.resx file, and they can be referenced correctly. I would gladly avoid Steve Baer’s workaround (mentioned in the same thread) if possible.

I’ve also seen this thread How to add icons with the vs 2022 preview of resource explorer and those linked inside, but they do not seem to help my case.

Other than this, the project works and compiles correctly. I am using Microsoft Visual Studio Community 2022 (64-bit) - Version 17.14.34. My project is targeting multiple frameworks: .NET Framework 4.8, .NET Core 8.0, .NET Core 8.0 - Windows.

Can anyone help me?

Ok, not a solution, but I found the newly imported resources were not added to a Resouces.Designer.cs file, so I added them manually:

After this, I was able to correctly reference them.

I understand this might well be a side-effect of migrating the project, but, what is happening here?