Are you sure the bouncing wasn't around on live? That sounds more of a terrain layout of the zone problem(its Mountainy) than a mob issue, and i think p99 doesn't alter the terrain maps much if at all if they can avoid it. As for the mobs bunching up only thing i can think of is train dispersal or mobs on a similar path spawning at the right time to make them path over the same area at the same time.
It may help if you gave them the mobs and the locations where you see them bunching up, that way they can verify the spawn timing/mobs on a cycle are set correctly
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