A few possibilities here. First, there could be a legitimate issue with the respawn mechanics that needs to be looked at. Second, you could be in an area that is too difficult for you. Third, there could be other people “in the area” that is affecting the respawn rate of enemies near to you. To really get this issue looked at, I would recommend that you post the area you are in, the level of the enemies, and your character level after dynamic adjustment.