So the solution seems to be to add
r.AllowGlobalClipPlane=True
into DefaultEditor.ini and DefaultEngine.ini files in the Project/Config folder and now the packaging works fine, it recompiles the shaders and planar reflections work in builds.
So the solution seems to be to add
r.AllowGlobalClipPlane=True
into DefaultEditor.ini and DefaultEngine.ini files in the Project/Config folder and now the packaging works fine, it recompiles the shaders and planar reflections work in builds.