Darius Ult Bug?

So im not sure how to recreate it so ill give a summary of what happened:

I was Darius against Malphite top, we both hit level 6 in the middle of a fight. I ulted first thinking it would kill him, Darius leaped in the air then did nothing and my ult went on cool down, Malphite realized he was still alive and immediately ulted me. When i landed my ult was off cool down so i tried ulting again and Darius did nothing so i died. I went back into lane, we got into another exchange that i was winning and i tried ulting again and Darius did nothing, i died. So i went back into lane and just tried to ult to see if it would work, it did nothing and i got dived by Malphite and Vi, i died.
So i reconnected ran up and ulted Malphite and it worked but then i almost immediately started lagging and then League froze for 7-8 minutes.

Not sure if anyone else is having this issue, but if anyone is please comment so i know it wasn't just me.

Oh and yes my R button was working, i was typing just fine.

EDIT: It happened to me again in the middle of a teamfight, i tried ulting and Darius jumped up as if to ult then did nothing, it went on cool down for 2-3 seconds then came back up, when i tried using it again nothing happened. This time i was able to use my ult after dying later on and coming back.