Simply for those who didn't know (which I didn't), Ubisoft added an XP cap to this FC game. One of those -- "Sure wish I'd known that from the start."
You hit it rather late in the game, and the "solution" if you wish to obtain additional skill points is to do all the remaining side missions which reward with a skill point. However if you were doing those side missions early on in the game, for a number of reasons beyond it simply rewarding a skill point, then you well might find yourself short the ability to gain enough skill points to get all the skills you either wish to have, or to simply get all the available skills provided in the game.
Can go into greater detail if there's interest, but at least wanted to let folks know about this "feature" which is new to the FC series.