I had the same issue today actually. If you right click the duplicate tab and hit "Close tab" that should get rid of it. Worked for me, now I just have the one GX corner again. It basically just opened a duplicate tab of the GX corner like any other tab, just without the little X to close it like all the others.
@gabriel-evaristo i have the exact same problem, for exemple when my youtube video is playing, it will lower my video game volume and i cant find out where to turn off this behaviour since installing OperaGX