Basically what happened was as I jumped to cut off Ashe's path, she threw out a volley at me, breaking the veil.
At the same time I was already in the animation for Aegis's stun.
Ashe ended up walking away with no stun on her as well as Pantheon being unable to cast any abilities. The abilities were on smart cast at the time so I tried to manually click on the abilities to cast but to no avail.
In the end what ended up fixing the problem was attacking an enemy champion allowing the abilities to be used again.