I think your anon may be right – maybe the Mulder heavy scenes are being shot first to give Gillian maximum time with her boys before they have to return to school and so her schedule is as light as possible right now? Would explain why no sightings of her on set and also give me hope that M/S together scenes are on the way soon!

Hm… I don’t know. We know Gillian was on set last week, and probably filmed a lot too. I don’t think that David filming one scene alone for a day means Gillian’s away having a break. She could have been filming somewhere else, indoor. Maybe today she’ll film alone and David’s off. Yesterday was probably just a few seconds of the episode, so I really don’t think it means much.