J4 Can't Ult a Spell shielded target!

We were defending our base when I was gonna make a play to kill their carry when I tried to ult her it did my ult animation but didn't put walls or do damage, the target had text pop up and said she was spell imune and my ult went on a 5 second CD. This must be a bug because J4 Doesn't CC his Target at any point during his ult.