Service module shrouds can't be disabled in VAB.

[TTSKarlsson]

When using this mod disabling shroud on service modules in VAB does nothing, so this mod prevents putting items/experiments inside those. (using 3.1.2)

[blowfishpro]

It's a stock KSP problem that ModuleManager makes worse, but still probably has to be fixed on the stock side.

If you really, really need to use KSP 1.6 with mods, let KSP load all the way to the main menu, quit, then let it reload without making any changes (and do this every time you change something in GameData)

[TTSKarlsson]

Thank you @blowfishpro , that workaround worked.