I joined in fine, and after about 5 minutes of flying around chunks loaded and such. Then I would get massive lag spikes that lasted around 10 seconds, then they would stop for about a second and start again.

the lag stops as soon as you press escape. and continues to load chunks like normal, but as soon as you resume the game it lags again. I have checked with previous versions if this was just my pc, but it isn't. it is in the snapshot.