I cant unlock the Achievement "Core Destroyer"

I got the game recently, but I cant seem to unlock the achievement Core Destroyer.
I have beaten the stage on easy, medium, hard, and insane. Is there a bug that is preventing me from being able to unlock it?

Are you sure you're doing the Correct "Assault"?

Not the "Assault Challenge Pack: Part 1, 2, and 3."

Just plain "Challenge: Assault."

Also make sure you're doing it in "Ranked" TrendyNet, not "Open"

Only things I can thing of atm.

I am doing the "Assault" not the challenge pack and I am doing it on ranked mode.

First Screen Shot is to show the trendy net icon.
http://cloud.steampowered.com/ugc/594718559832831196/95E6976CE2B64F49E7CFD22807D5E6CF3B3FE533/

the second screenshot shows that I have completed the challenge on hard.
http://cloud.steampowered.com/ugc/594718559832865815/A495CCB57E51EF92079165A784F04DA08CF2A6C0/


Next screen shot is the Core Destroyer Trophy is in my tavern
http://cloud.steampowered.com/ugc/594718559832930572/4A605D2DC328092656B7E2CB97AFB56E35AB3A36/

Lastly, this screen shot is my achievement page, and it is showing me that I have not unlocked the achievement yet.
http://cloud.steampowered.com/ugc/594718559832940245/DDEB25611E4C32496E2BFE3145014E4E7AB85E4A/

I've had the same issue as you, but I can't unlock any of the new achivements. And the developers do nothing about it ;(

I wasn't able to unlock any achievements for nearly 2 months now. They finally started unlocking about a week ago with no real hint as to why.

I hate to ask because I assume you are in Ranked, but were you in Ranked or Open/Local? Did you export your data to local/open and then complete this challenge there?