Sometimes btAssert failed on btSequentialImpulseConstraintSolver.cpp Line: 1265

[anchurcn]

fsum is zero, I don't know what I did wrong.
I use coneTwistConstraint to connect two rigidbody with capsule shape for ragdoll.
If the the angular limits is zero, the exception is shown almost every time when add ragdoll to world. But with the limit increase, it will show rerely.

The problem is shown when add ragdoll to world, if I press F5 to continue, the simulation will go on. And seems everything is ok.
Do I need to provide more infomation?

/* Partial btSequentialImpulseConstraintSolver.cpp*/
///finalize the constraint setup
	for (int j = 0; j < info1.m_numConstraintRows; j++)
	{
		btSolverConstraint& solverConstraint = currentConstraintRow[j];

		if (solverConstraint.m_upperLimit >= constraint->getBreakingImpulseThreshold())
		{
			solverConstraint.m_upperLimit = constraint->getBreakingImpulseThreshold();
		}

		if (solverConstraint.m_lowerLimit <= -constraint->getBreakingImpulseThreshold())
		{
			solverConstraint.m_lowerLimit = -constraint->getBreakingImpulseThreshold();
		}

		solverConstraint.m_originalContactPoint = constraint;

		{
			const btVector3& ftorqueAxis1 = solverConstraint.m_relpos1CrossNormal;
			solverConstraint.m_angularComponentA = constraint->getRigidBodyA().getInvInertiaTensorWorld() * ftorqueAxis1 * constraint->getRigidBodyA().getAngularFactor();
		}
		{
			const btVector3& ftorqueAxis2 = solverConstraint.m_relpos2CrossNormal;
			solverConstraint.m_angularComponentB = constraint->getRigidBodyB().getInvInertiaTensorWorld() * ftorqueAxis2 * constraint->getRigidBodyB().getAngularFactor();
		}

		{
			btVector3 iMJlA = solverConstraint.m_contactNormal1 * rbA.getInvMass();
			btVector3 iMJaA = rbA.getInvInertiaTensorWorld() * solverConstraint.m_relpos1CrossNormal;
			btVector3 iMJlB = solverConstraint.m_contactNormal2 * rbB.getInvMass();  //sign of normal?
			btVector3 iMJaB = rbB.getInvInertiaTensorWorld() * solverConstraint.m_relpos2CrossNormal;

			btScalar sum = iMJlA.dot(solverConstraint.m_contactNormal1);
			sum += iMJaA.dot(solverConstraint.m_relpos1CrossNormal);
			sum += iMJlB.dot(solverConstraint.m_contactNormal2);
			sum += iMJaB.dot(solverConstraint.m_relpos2CrossNormal);
			btScalar fsum = btFabs(sum);
			btAssert(fsum > SIMD_EPSILON);
			btScalar sorRelaxation = 1.f;  //todo: get from globalInfo?
			solverConstraint.m_jacDiagABInv = fsum > SIMD_EPSILON ? sorRelaxation / sum : 0.f;
		}

		{
			btScalar rel_vel;
			btVector3 externalForceImpulseA = bodyAPtr->m_originalBody ? bodyAPtr->m_externalForceImpulse : btVector3(0, 0, 0);
			btVector3 externalTorqueImpulseA = bodyAPtr->m_originalBody ? bodyAPtr->m_externalTorqueImpulse : btVector3(0, 0, 0);

			btVector3 externalForceImpulseB = bodyBPtr->m_originalBody ? bodyBPtr->m_externalForceImpulse : btVector3(0, 0, 0);
			btVector3 externalTorqueImpulseB = bodyBPtr->m_originalBody ? bodyBPtr->m_externalTorqueImpulse : btVector3(0, 0, 0);

			btScalar vel1Dotn = solverConstraint.m_contactNormal1.dot(rbA.getLinearVelocity() + externalForceImpulseA) + solverConstraint.m_relpos1CrossNormal.dot(rbA.getAngularVelocity() + externalTorqueImpulseA);

			btScalar vel2Dotn = solverConstraint.m_contactNormal2.dot(rbB.getLinearVelocity() + externalForceImpulseB) + solverConstraint.m_relpos2CrossNormal.dot(rbB.getAngularVelocity() + externalTorqueImpulseB);

			rel_vel = vel1Dotn + vel2Dotn;
			btScalar restitution = 0.f;
			btScalar positionalError = solverConstraint.m_rhs;  //already filled in by getConstraintInfo2
			btScalar velocityError = restitution - rel_vel * info2.m_damping;
			btScalar penetrationImpulse = positionalError * solverConstraint.m_jacDiagABInv;
			btScalar velocityImpulse = velocityError * solverConstraint.m_jacDiagABInv;
			solverConstraint.m_rhs = penetrationImpulse + velocityImpulse;
			solverConstraint.m_appliedImpulse = 0.f;
		}
	}