Labeling in AGOL gives me inconsistent results. It seems to work with one map service, but not another seemingly identical one.
Now you see it:
http://bit.ly/1CPxN1s
Now you don't:
Illinois Floodplain Maps - FIRMS
On a seemingly identical application, now you see it:
http://bit.ly/1CPy7gC
Now you correctly STILL see it:
Illinois Floodplain Maps - FIRMS
Granted by the time you read this post all 4 links may be showing labels, but as of writing on 3 do.