Ult doesnt work :/ (multiple champions?)

While in my ranked game i was unable to use my ultimate ability, i thought this had to do with my controls but my teammates started to have the same issues. It looks like you can sometimes use it but most of the time it just doesnt work, and no my ult wasnt on cooldown and yes i did have the mana for it. I dont know if this is champion specific but it happened to me Fizz and my teammate Graves. pls fix