I think it was from the phoenix event that lasted for 12 days where we used to destroy boxes and we had to enter everyday to get the achievement last spring. It was a one time only thing so maybe you missed it by a few days?
Its from an android exclusiv droid event held in spring 2016. If i remember correctly it’s difficult to remove acchievements that are linked to google play.
Replies
Let everyone finish those achievements.
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/117958/12-days-of-spring-dev-commented
This.
It has changed since then. It's tied to the 7* Wicket achievement. https://forums.galaxy-of-heroes.starwars.ea.com/discussion/comment/1706270#Comment_1706270