I think they did some testing and found issues. I think next update will fix those issues. I’m guessing but it seems likely.
You used to get PvP score points for winning GW battles, so GW and PvP had to be connected somehow. In the new PvP, setting of defences was removed, and without the ability to set defences GW is pointless. Seeing that GW is delayed again, and again, it clearly means that GW system used some of the code used to make old PvP work. Maybe it was the setting of defences part, OR some other part that we can’t easily notice from the outside. It’s a normal practice to have different systems in software use the same parts of the code, so that you don’t double up on coding the same things, which could cause separate problems on its own. But now that old PvP is replaced with this new one, and we all see that the new PvP is not exactly working entirely as intended, and possibly this affects GW in some way, causing problems. Seeing how emotional people are getting about GW, it’s better to wait for next GW that will hopefully be working as intended than to have it, but be mostly broken.