This isn't a bug. On cartridge, Urshifu in preview shows up as this sort of neutral Urshifu forme that visually doesn't look like either Single or Rapid; it has no in-battle animation and exists solely as said preview sprite, meaning it's not visually possible to determine the Urshifu forme at preview. Since it has no battle animation, it would be a notable visual discrepancy compared to anything else when implemented on sim, so Urshifu-S is instead treated as this neutral (ie; the mon is treated visually as Urshifu-S until proven otherwise).