Galio ult not working properly, must be bug

I was Galio in a ranked game on EUNE. I flashed and ulted, only Katarina (enemy team) was in range. And yes, I know you will ask, she 100% was in the ult range, even though she was kind of close to the max range. But wihtout using QSS or similar item (or item from someone else in her team) or summoner spell she just walked out of my ult. It didnt affect her at all. In chat she and others in her team responded "bug" and "ty rito", so I am not the only one who saw it.