A couple of the shuttles were cancelled due to a loss of signalling at Brighton. The buses did leave at the same time, but 1 was fast and 1 was a stopper.
There was reduced line capacity due to the work, hence why an hourly shuttle ran.
Rail works are VERY complex and cost a hell of a lot of money and are planned to a tee, they MUST take place during the night as there is no other time - even during a full weekend possession. If the work overnight isnt done, then you can be certain work WILL overrun onto Monday morning.
Also...