Same here. In had the skill unlocked, but the previous one wasn't, where you had to take two outposts without being detected. I then unlocked the previous's skill, but didn't have enough skill points to get both. At this point I had karma level 6. I then hosted a coop Game with a friend who had karma level 2, and it locked me out of that skill, saying I needed 4, and I was 2 below. It still says this now I'm not co-oping. Bummer.
Not sure if this will work if your maxed at Level 8 on Karma, but if you go around killing civilians and/or Golden Path members you loose 50 Karma points for each "murder" of the innocent that you commit. So you could, in theory, go on a killing spree of the innocent and lose a ton of karma to take you back to level 3, then get to level 4 again. Just an idea as I have not tried it. Not sure if you can go back an entire Karma level or not, but worth a try.
Well I am on pc and this bug is still not fixed, it's so sad, we are in 2017 and I can't get the 100%
https://gyazo.com/67da7111540e32f9ff7f6f5b4d9311a7
not only vavle did this with cs:s and team fortress but now ubisoft... comon <.< 99% !!! grr :P
please fix it ubisoft - there is no way I can get back my levels down (cause it's glitched over, and so is the karma level)
https://gyazo.com/ac6372c31e9e47be3ff7bfb95d410a11
oh well..