A bug that's affecting League of Legends champions' ability leveling has been noticed on the PBE and is currently being examined for a fix.
The issue essentially halts players from leveling up an ability. What's worse is that it takes the ability point away as if you had actually leveled up a skill but leaves you without an upgraded ability. The skill point will be returned eventually, but it's still a setback for early games when having all of your abilities is key for the first few fights.
"The team I am on is currently trying to track down a bug that happens pretty infrequently," a PBE update from Riot Afic read. "Basically, if you try to level up an ability, sometimes the ability point will be used, but you won't have access to the ability (ex: you can be level 1 with no skills). When you level up again, you will have access to 2 ability points (so basically the ability point is wasted for an entire level)."
Within the same PBE announcement, the Rioter requested that anyone who encounters the bug share information regarding the issue so that it can be taken care of.
"If you encounter this issue, any information you provide can be useful (what was happening when you tried to spend the skill point, did you press the hotkey or click the skill icon to level up, what champion were you playing, etc.)," the Rioter continued.
"I will be checking this thread frequently and likely reach out to anyone who encounters this bug. Thanks for any help you are able to provide!"
Several players already commented within the PBE post to share their experiences with some recounting instances where they'd seen their ability point be taken without being used correctly. For the time being, it appears that this bug is locked to the PBE servers and isn't impacting live games in any way, but squashing the bug on the PBE through further testing will make sure that it never has a chance to affect anyone's live games.
Check the PBE post on the forums to see more updates and to offer any help that you may have if you've encountered the leveling bug.