Because V4.2 morphs have the wrong vertex count.
That's why V3RR's morphs don't work with V3, and vice versa.

Inside D|S, each LOD V4 can automatically use V4.2's morphs, but in Poser you need a separate set of morphs for each LOD stored in a separate cr2.

And, as the SetUp room not just transfers the bones but also morphs, you first have to delete the original V4.2 morphs from the LOD's cr2.

Then use the script to transfer the morphs of a fully injected V4.2 cr2 over to the LOD cr2.
(But as several of V4.2's face morphs are just ERC dial settings, you first have to spawn actual morphs for them, because the script can only transfer "real" morphs)