hey i got this one too . but mine was when i reached level 13 and upgraded my ability , in my case (mug) coz I'm a thief, i was upgrading it to tier 3 and it just can't, it just stays in tier 2 of the ability and suddenly when i got into combat, i can't pick the mug ability, it just disappeared after that. I tried loading another save and tried to upgrade the ability (back stab) and it did the same thing . it can't be upgraded and it disappeared during combat and the same applies to other abilities . i can't find any solution for this, i thought i was alone and then i saw this post .