I've had the same problem on my 50 Guardian, I'll have 4 mobs standing right next to me and i'll only hit 1 or 2 of them. Heck, I even went back to Tython and had 3 level 6 mobs standing less than 2m from me and I only hit 1 of them, and they were right in front of me. Yeah, they broke something with Force Sweep in the last patch.