Multithreaded with constraint

[MakotoChiba]

When I use multi threaded solver with a lot of constraint, it get crash.
I set
collisionConfiguration = new btDefaultCollisionConfiguration();
dispatcher = new btCollisionDispatcherMt(collisionConfiguration, 40);
solverPool = new btConstraintSolverPoolMt(BT_MAX_THREAD_COUNT);
parallelSolver = new btSequentialImpulseConstraintSolverMt;
overlappingPairCache = new btDbvtBroadphase();
overlappingPairCache->resetPool(dispatcher);
dynamicsWorld = new btDiscreteDynamicsWorldMt(dispatcher, overlappingPairCache, solverPool, parallelSolver, collisionConfiguration);

Thousands of rigidbody objects(box) works greatly. And with small amount of constraint(btGeneric6DofSpring2Constraint) is works as well.
But when I use many 6dof (it around over 50), solver happens error.

Do I need something for many amount of constraint?
I tried to check same scene with no-MT solver, it works.

[MakotoChiba]

Oh, this problem is happening only on dev build from repository.
I back to 2.88 release build, it has no error.