I get the same error at the shopping scene for Aida before traveling to go to the Koi game even after changing the sizes. I had gotten the beach scene all the way through at size 4 and the next scenes until the shopping scene at size 4 & 5, but i have the size at 5 and 6 for the shopping scene, the error pops up and will not go away unless i close the game
As I already said before, the game isn't designed around changing sizes whenever you want via Debug Mode. This feature exist for a different purpose and some of the scenes might not work correctly as they have unique assets which depends from a correct size being set that is available through just playing the game and unlocking sizes as it was intended.
Beach scene on Aida's arc will work only on size 3.
Shopping scene and Kanagawa arc will work only on size 4.