That's because I'm lazy and haven't completed it/or haven't handed it off to uploadIn VGC 2018 Incineroar's Shiny sprite is only Shiny when being viewed from opponents side of the field and is never shiny from the back even in replays when field side is switched.
EDIT: In my experience I have used mobile phone; Android to access Pokemon Showdown only to revive this error.
not a bug
that applies to most SM shiny backs, since they aren't completed/uploaded
That isn't exclusive to VGC either.