As shown in the attached image, Jinx's level 3 mastery (Might be others, only champ I have at 3) bar is incorrect. According to the numbers I am half way through my level 3 mastery but it only shows about a quarter way full. Think that about sums it up...
Not a bug, the points carry over per level so the points that come over are basically your starting point. like say it's 6000 to get to level 3. you're now basically at 0 points gained on the way to 4. So it looks as if you've only got 1100 points so far. This is just the total amount of points you have gained through the levels.
I don't think it's an error. From what I can tell, instead of resetting to 0 on level up, it continues stacking the count. The bar is based on the number for the last level up as 0, everything after that is included on the bar you see. So, your bar is accounting for only 1,162CP.
It takes 6kCP to reach level 3.
The bar is for the level itself is the current level while the xp is the total.
Ah, I see, isn't that a little confusing. Well nvm then.
I have come across what seems to be the same issue Link to my bug report
