Why only sub anim instances check duplicated slots?

In my team, we are using sub anim instance for gun animation.
When we compiled parent anim instance, there is a warning that indicates duplicated slots. (by ProcessLinkedAnimGraph function and bCheckForCycles parameters)
But that warning happens only when we use same slots in sub anim instance.
On the other hand, there is no warning when we use slots have same name in parent anim instance.

The warning warns that if we use duplicated slots, there will be problem. but we use it sometimes and it seems like works well.

This is example image.

If this graph exists in parent anim instance, there is no warning. but if it exists in sub anim instance, there is.

Could you explain why?