Zyra bugged e stopping when cast close to a minion

Have been playing Zyra mid recently and have repeatedly had a bug where I walk to the front of the enemy minion wave cast e and upon hitting the first minion the e just vanishes and doesn't damage or root anything else. I can't reliably reproduce this bug (although is usually happens at least once every game) and don't have a recording (I don't record my games).