What you were expecting to happen, and what actually happened?
When I selected a character to use their power, the popup was invisible. The button still worked if I guessed correctly where it was, and the gems were unclickable as is they were covered by the popup, but there was nothing displayed
What are the steps to make it happen again?
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
Also, when I restarted the game to try and fix it I found that you get kicked out of any game in progress and it counts as a loss in arena. That was a nasty surprise. Restarting did fix it though.