Hello,
This is due to how barriers interact. Attempting to put up the same barrier twice in a row causes the barrier to fail. I will contact the devs and ask if this is intended or not and return with more information once I know it. Thanks!

YujinTakara is correct. The mystery cannot "half activate." it either activates in its entirety or it does not activate at all. Since the barrier is already present, when you cast the mystery a second time, you are cancelling the barrier and cancelling the mystery. As mentioned, I am looking further into this issue to see if this is intended or not. I will let you know once I hear word back.