Hi and welcome to the Community,
Kind of strange with an hemi pointing upwards. I eventually saw something like this with a dir light but here 
Though, what about this light ‘range’ parameter for your hemi. I can see in SS is set to 1.79*… Could it be that from the export this value would be below the scaling of the scene in BJS? Or could it be that it’s a right-handed vs left-handed issue and the light would be actually pointing down? trying to guess here and btw, you wouldn’t happen to have a PG to share?