There normally is always update button on Boss Invasion but..
I managed to broke it, so what I did was: I was simply were battling boss on another boss, and I went on second tab to Boss Invasion as well. However, I tried clicked Attack and got "Stop cheating" and update button as well.
There's no update on the new prototype when your boss is still alive, only once your boss has died (or when expired if I remember correctly). This will be a non-issue as soon as old global boss is removed.