My speculation is that its due to shrinking player numbers. I often end up in UK, Australia, etc servers when joining missions via matchmaking, where enemies rubberband a bit or just straight teleport around. This is even more evident in the DZ, when players behave that way or you're "reloaded" in the checkpoint rooms 3 to 5 times before being allowed to enter the DZ.
Any news on this issue yet? I still have the periodic framedrops/lag every 15 minutes or so. Tried so many things suggested on this forum, that I am out of ideas. Since it's tied to TU12 I really can't understand why Ubisoft didn't fix it already. i mean, I could play without any problems until TU12.