I've gotten all the achievements of the game, except this one. It says 'Clear 20 stone slabs using long chains', and I'm pretty sure I've cleared as much by now.
Do I have to clear them with ONE chain? Or in one level? I figured it couldn't be that difficult as some 43% of all players on Steam have this achievement, but somehow it won't work for me.
Any ideas on what I am missing, or how I can complete the achievement?