I'm not sure why, and this may be an issue on my end, but I'm experiencing really, REALLY high latency on the modpack server (with my internet fine otherwise, of course). I'm talking 5 seconds to break a block. I thought I didn't have permissions at first. The only thing that I can think of is that whoever's started building is already quarrying (I assume that's you), but I don't think one quarry would do all of this.
[Edit] I just thought of this, there is water in the bottom of the quarry-hole that this person's building in. Could that be it?
[Edit 2] Well, I went down and looked. I'm at least confident that the water's not helping. It's flowing into nooks and crannies, inside the main body of water there are seemingly random pillars of air all throughout, and for some reason the water isn't even flowing normally from one quarry-hole to another. It's made this big wall of water. Shit's jank, yo.