There are two main reasons why multiple canvas renderers are required:
1) There are multiple atlas pages required in the current animation frame.
2) There are multiple slot blend modes used at your skeleton in the current animation frame.
So please check your skeleton if you have accidencally set any slot blend modes in your Spine project (other than Normal and Additive which can be drawn in a single draw call). You can check this out in Unity by having a look at the SkeletonData asset, in section Blend Mode Materials. When using the SkeletonGraphic component, there is also a section of Blend Mode Materials for this SkeletonGraphic instance (this is necessary since canvas renderers don't use normal Material references).
From your second related thread here:
One of my SkeletonGraphics needs Multiple CanvasRenderers set to true and generates 4 additional renderers. They show with a plus cause they are not yet added to its prefab.
The prefab itself does not even generate as many, only one.
The prefab should have the same number of CanvasRenderer children. If that's not the case, then this behaviour is indeed strange. Could you please send us your problematic exported Spine assets? You can send them as a zip package to contact@esotericsoftware.com (briefly mentioning this forum thread URL so that we know the context), or attach it to a forum posting.
