So in roughly half the map in Alternate Metropolis in the Brothers in Arms instance, if you're unlucky things are laggy as heck and cause disconnects. I haven't seen this explanation posted here yet, so here's my theory: An accidental double- or triple-spawn of all the adds, both allied and enemy, around one of the briefcases needed. In the northeastern (I think) corner of the zone where you're looking for briefcases, when my group went there today, there was a crazy amount of both friendly mobsters and hostile Lexcorp troops. It got pretty amusing, actually, as all the mobsters would repeat their few lines over and over again while flocking around the briefcase point. Sing it with me, kids. "The protection racket is BADlegitimate business. You'd better set the Don freebetter set the Don free. You beyou'd better set the Don freeyou'd better set the Don free. You'd beGo totter set the Don frGo to hell. Go to heYou'd better set the Don free."