I don't have a screenshot of this, but ever since the last update 
Rakan's E can't be recast without enough mana.
It also says the same for his Q after hitting someone with it if you don't have enough mana (even though it doesn't need to be recast)
Boltonator1 votesRakan’s Q can’t be recast though.
As far as his E is concerned I have seen this bug and can confirm that if the first cast of E puts Rakan under the minimum mana barrier to cast it (as though he were casting it for the first time) then he cannot recast E.
This bug seemed to come with patch 9.7.
s u n g 71 votes
Yoloyiff1 votesBumping, this has nearly gotten me killed a few times.
