>>52566813It seems as though the change may only be obvious if you actually set the Pokémon as your buddy.
I'm not about to set these Ursaluna as my buddy, but they counted as XXS and XXL before the update went live. I had a Gothita that was XXL at one point but traded it away because shit doesn't matter, and one of my Houndoom changes to XXL when mega evolved.
The "New record" that overlays the screen when you look at the recently caught Pokémon summary is actually pretty annoying desu.