Just had it happen on my seasonal Tech Adept.

Actions taken right before it happening:

I leveled to 94, assigned my skillpoint, then completed the missions at Merciful Agony MXCII. I then proceeded to purchase all of the options they had available (+1 attribute point, +2 skillpoints, and the innoculator component). I assigned the attribute point and then the two skill points, and it instantly put me at -1 skillpoint.