Not sure if any one else has seen this happen to them, and I am not entirely sure it is meant to happen this way.
I believe there might be two issues happening, I'll write out both.
Basically, when zipping a Sculpt Normal Layer the Normals will turn into having a grey outline (which I believe is intentional), however it only turns grey if the effects icon is "on" (eye symbol) in the Layer channel, and turning the eye symbol off causes the Bevel and Emboss to appear on them. In my opinion it is the wrong way around. When the eye is off it should have the grey outline, not the other way around.
The second issue is if the sculpt layer has duplicates inside of the same folder, after zipping and then unzipping that file causes the duplicate Normals to disappear, however they are still visible within the folder in the Layer Channel?
Create a new layer
Select the Sculpt Tool
Create a sculpt of some sort
Duplicate the sculpt that was created and move them to a different place
Zip the Folder containing the sculpts
Once Zipped, Unzip the folder
Observe that the duplicate normals disappear, but are still visible in the folder
The duplicated Normals should still be visible within the folder and on the normal map after being unzipped.