[Gameplay] Zac's 'E' won't upgrade!

So I was playing the new Zac and I had just gotten to level 5 and didn't upgrade an ability because i was fighting. When I died I went to upgrade me 'e' and it wouldn't. It instead ate my skill point and didn't upgrade the ability. Now the mark to upgrade my 'e' is frozen over the ability. I did get to upgrade it afterwards but my skill point was still eaten and i wont ever be maxed out.