There's a bug in the Colosseum Fight. When you start the fight, on Android, there only interact and menu buttons present... Not shoot option (X).. I tried but can't kill any zombies due to it and the spikes aren't activating either.
I was having this same issue. But I fixed it by pressing the down arrow at the middle of the screen, then my shoot button(X) appeared. I hope this helps someone that finds it because after days of googling I just got lucky and figured it out
