I can confirm the packaging issue. I have tried a few different possible solutions without success.
The main difference, and possibly the root of the problem, is that unlike earlier versions, for 4.23 the original UE4Editor-RHI.dll needs to be overwritten with the file that comes out of building from source. @YujiangW himself was the one who graciously informed me that this is necessary.
While the source code modifications to the editor, that allow GPU Lightmass to work, do not touch (AFAICT) UE4Editor-RHI, apparently the version that the compiler produces on my end is somehow different from the original.
Unfortunately, I do not know enough about the details of cooking, packaging and the shader compiler to be able to diagnose/fix the problem on my own.
If having to switch between the original and modded version of the editor is too much of a hassle, some might find it easier to build from source using my fork.
I have tested and can confirm that packaging using a locally built, from source, version of UE4 works just fine.