Hmmm... I did unlocked it. So it's not "bugged".
I was with another guy taking care of the small gummies while the other two fought for the big one. The only difference I see it's the other team didn't even got score the big gummy. But I don't think this is the condition. It's quite difficult (We did it tho. So lucky).
At least I can say there's no problem your team touching the big gummy. It would be impossible if not, with 3 big gummies you win. And you need a looooot of small gummies to win.
Are you sure your team didn't scored the big gummy? 🤔
Let's see other people experiences...