Skill gem unable to use

I have enough attributes for Shockburst round skill gem, but after i changed my weapon i can't put the skill to skill bar.

Not even showing stats for the skill gem.(thing that shows when you click > button)

Yes i checked stat for skill and support gems.

However when i put in new same level 19 Shockburst round it works, but when i put in my 6 link Shockburst round skill, skill does not work and not shwoing stats of skill.

What am i missing here?