I don't exactly have the equipment for videos, but all I can say is that pre battle menu loads for all the other bosses except those two, cause for some odd reason they skip straight to the fight without me changing my setup for the fight. I tested it by restarting the phantom fight and it still didn't load, also to clarify it was during story mode at the time before I fought megadragonbowser. By the way I just went through it again and the preparation menu not loading seems to only happen to the world bosses outside of the wash time machine where the preparation menu loads for the rematches with Rabbid Kong, Icicle Golem, Phantom, and MegadragonBowser.
https://www.nintendolife.com/news/20..._battle_update
I couldn't do a video but will an image work? Anyway the image from the url doesn't show for the world bosses, any reason why?
If the image doesn't help for you then perhaps the video url wil.
https://www.youtube.com/watch?v=9gA5DNs85fE&t=117s