Twitch with runaan's stops his ulti from activating corrrectly

Just played a TFT game where twitch's ult stopped after 1 auto and reset his mana bar only if runnan's is placed on him. Link to a the same bug on EUW: https://boards.euw.leagueoflegends.com/en/c/bug-reports-eu/iVik3yIt-tft-twitch-runaans-still-broken