It indeed is not possible to have duplicate name (sorry). I’ll see how I should improve this, but in the meantimes, you can use another name (and sorry for taking that long to answer)

The Canvas Atlas contain information about the different element in the canvas, on the same model (and code base) than what is used for the r/place atlas.

More information is present in the announcement post at https://toast.ooo/post/4202022