Went all skills used, i use black spirit skills 30% buff some how get +10k cp. As picture

Not a bug, but a feature. You probably didn't notice killing those lightning firefly thingies (forgot what they're called) Just before or coincidentally during the time you used black spirit skill. It gives you a huge boost in CP around 10k+ to deal additional damage to the boss during its lightning element transition.

EDIT: Just checked your screenshot again. It says "Defeat Lightning Spirits" on the upper right. So most probably, you killed a Lightning Spirit and managed to get that 10k+ CP boost temporarily.