Can't add sub-graph input to my anim state in BP

Hello,

Long time ago I created this sub animation and I used “sub-graph input” for it. As you see on image below:

Now I am trying to create anew animation following the same concept but I can not add that input anymore, is not listed anymore. I can’t even copy it.

253045-renderpeople-ericthirdperson-animbp-9-7-2018-5-03.png

Did I forget any step? Any idea what could be happening?

FYI.
I solved this creating new animation instances, apparently you can only have one sub-graph input per animation instance.