Looks like the mesh folds and is intersecting with its own folds.
Try lower resolution mesh, and put folds in a sisplacement map.

When a cloth sim makes the mesh intersect with itself the only way out is to stiffen the cloth (reducing the folding) or go lower res mesh and with a displacement map.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
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