MCVE is here, forked from the nqueens example: https://github.com/vilmosnagy/optaplanner/tree/mcve/multi-threaded-solution-hangs If you start the example app and try to run the NQueens example, it'll hang. But if you set this property to true, then the custom MoveIteratorFactory will generate an Iterator with some NoOpMoves (instead of the empty iterator; the NoOpMove is an empty AbstractMove , which does nothing)  and the first localSearchPhase  ends normally. Or if you set the moveThreadCount to NONE, then the first localSearchPhase ends normally as well.