[=Kenomica;237526]
I have done, thanks. Updated the post with all the newly found information to hopefully help fix the.
Glad to hear your problem was fixed 
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Kenomica/others - did you discover any workaround for the instanced mesh?
I tested further today and found that using a proxy object/blutility to spawn instances doesn’t work either; the moment you restart the editor any instances spawned outside of a construction script seem to be cleaned up (and to quickly recap the original bug, any instances spawned within a construction script cause the editor to crash on load after lighting is built). Looking at InstancedStaticMesh.cpp I see code specifically to handle lightmaps for instances created in construction scripts (eg: FLightMapInstanceData), further debugging may yield clues on the crash or a workaround. Probably best to have Epic look further though, I’ve bumped your answer hub post for comment from Devs.
To move forward for now I’ve moved all procedural foliage to ‘Begin Play’ and will apply dynamic lighting if feasible.