Pantheon's W (stun) did not come out

My id is Shiina Mashir0, On March 23rd, a game ended at 2:36 pm, I fought with Darius top lane around LVL 9. AFTER Darius finished his E (pull), I autoed him and tried to stun him. However, the stun did not come out, but I jumped to him and my W went into CD. There was not any factors that could cc me at that time, and there was no minion around. Even Darius thought this must be a serious bug. I think this is not the first time I faced this problem. I am a pantheon main, and there were many times that the stun failed (not be cced or sth, it must be a bug). The BUG IS SERIOUS. STUN is IMPORTANT TO PANTHEON, PLEASE FIX IT, THANKS!!!!!!