Spent the weekend playing in Wardin which was loads of fun. But several of us noticed significant lag when building on the sky islands. So much so, a placed block would show up several seconds later.
However, when building inside one of the ground islands, there was no apparent lag.
Also, when I was building bridges between sky islands, periodically I would place a block, it would show up and then vanish. This would repeat continuously in subsequent tries. But after, doing something else for a short time, it would work. It was pretty thrilling building the bridge up that high over the lava. 