Feed The Beast

I've been playing FTB Endeavor with friends, and recently we've been encountering an event where when two of us are close together for a period, a purple cloud will spawn in our vicinity, and hostile mobs from several mods will spawn, at the same time removing all light sources (and applied energistics fluix cables) in the immediate area. Could someone let me know which mod is causing this, and suggestions on how to prevent it? Much thanks.