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I think when like 5 or 6 joints touch the ground at the same time there is no DQ but am not sure about that.

When there are alot of things touching each other (hands/joints/ground touching hands/joints), the game just doesnt notice new contacts being made, this is probably to prevent the game from lagging in some way.
Just changing the maxcontacts in the setting to something higher already decreases the chance of getting the 'bug' alot.