For This One, You Have To Beat A Deep Dive At "Challenge Rank 10".
You Must Beat 10 Deep Dives To Raise Your Level To 10, Before Beating Another For This Achievement To Pop.
- Current Solo Challenge Level Is Displayed On The "Season" Tab In Your Journal.
*Side Note*
I Got This One In A Group Deep Dive, So After Your Solo Rank Is 10, The Next One You Do Should Pop It; Regardless Of Whether You Do The Next On In Solo Or In Group.
Good Luck!