Code Not Working On Different Devices

There's an app i'm currently working on that works differently in each device it is installed in. For example, the login doesn't work for androids that seem to be new, while it works fine on old devices. I'd like to know why exactly this happens, is there something I need to setup on player settings, or do i need to install something i'm forgetting? I fail to undestand why it works well on the editor but not on the build