After You Failed. Why?

Hello,

I recently was in a match where I was mirroring Clefairy and Calyrex-S. We were in the third turn of Trick Room. We both coincidentally had Clefairy and Calyrex-S out with the same moves I'm assuming. I used After You on my Calyrex-S (Non-Terastallized) and my opponent did as well. Except, my said it failed while he got his After You through and KO-ed my Clefairy and Calyrex.

What happened there?