Prefab variant from FBX sometimes loosing lights and connections.

Hi, I am using Unity 2019.1.0b4 and having intermittent problems where after re-exporting my FBX from Maya certain aspects of my prefab will vanish. This is primarily happening with lights (added to the prefab variant) and with materials remapped in the FBX. I can understand that remapped materials might be getting over-written when I update the FBX, that is fine as I can simply reassign them. The missing lights on the other hand should not be changed as the prefab variant only references the FBX file. I would be interested to know if this is a problem with my workflow (shown below) or a possible bug that I am experiencing.

INITIAL SETUP

1. Maya LT, build model, assign shaders, setup animation ...
2. Export Model and Animation to Unity in a single file, (says new in Maya LT 2018)
3. Unity, select prefab, remap Maya shaders to my own unity materials, "Apply" Settings.
4. Unity, select FBX and create Prefab Variant.
5. Unity, Open prefab, add and position point light gameObjects
6. Unity, Create animation controller and assign to prefab
7. Unity, Close prefab
8. Unity, Drag prefab into scene, position as required.

MODS TO MODEL OR ANIMATION

1. Maya LT, Open Maya LT
2. Maya LT, Import an FBX file from a Unity project and auto-configure for exporting
3. Maya LT, make required changes to model / animation.
4. Export Model and Animation to Unity in a single file, (says new in Maya LT 2018)

Much appreciated.