SofaPython Monitor error with MechanicalObject

Hi guys, nice to meet you all.

I’m working a little with Sofa, in particular with SofaPython, to model an interaction between a needle and a phantom (actually just the first layer, the fat). I was able to model the interaction with also an insertion of the needle, and now I need to create a graph showing the forces during this interaction. To do so, I’m trying to use the Monitor component. This works if added to the Fat node but, if i try to add it at the needle node, Sofa keeps crashing with an error

[Monitor] error : no MechanicalObject found

even if the MechanicalObject is actually present. This is the needle node creation code:

# ==========================
# NEEDLE NODE
# ==========================

meshFile_needle = 'data/syrette2.obj'
scale = 10
        
needleNode = self.rootNode.createChild('Needle')
needleNode.createObject('EulerImplicitSolver', name='ODE solver', rayleighStiffness=0.01, rayleighMass=1.0)
needleNode.createObject('CGLinearSolver', name='linear solver', iterations=25, tolerance=1e-7, threshold=1e-7)
needleNode.createObject('MechanicalObject', name='mechObject', template='Rigid3d', dx=20, dy=150, dz=-50, rx=0, ry=0, rz=-90.0, scale3d=[scale, scale, scale])
needleNode.createObject('UniformMass', name='mass', totalMass=1)
needleNode.createObject('UncoupledConstraintCorrection')

### MONITOR ###
needleNode.createObject(
    'Monitor', name='monitor-displacement-faceNode', indices=45, 
    template='Vec3d', listening=1, showPositions=False, PositionsColor='1 0 1 1',
    ExportPositions=True, showVelocities=False, VelocitiesColor='0.5 0.5 1 1',
    ExportVelocities=False,showForces=True, ForcesColor='0.8 0.2 0.2 1', 
    ExportForces=True, showTrajectories=False, TrajectoriesPrecision=0.1, 
    TrajectoriesColor='0 1 1 1', sizeFactor=0.1)

# Visual node
needleVisNode = needleNode.createChild('VisualModel')
needleVisNode.createObject('MeshObjLoader', name='instrumentMeshLoader', filename=meshFile_needle)
needleVisNode.createObject('OglModel', name='InstrumentVisualModel', src='@instrumentMeshLoader', dy=-2*scale, scale3d=[scale, scale, scale])
needleVisNode.createObject('RigidMapping', name='MM-VM mapping', input='@../mechObject', output='@InstrumentVisualModel')

# Collision node
needleColNode = needleNode.createChild('CollisionModel')
needleColNode.createObject('MeshObjLoader', filename=meshFile_needle, name='loader')
needleColNode.createObject('MeshTopology', src='@loader', name='InstrumentCollisionModel')
needleColNode.createObject('MechanicalObject', src='@InstrumentCollisionModel', name='instrumentCollisionState', dy=-2*scale, scale3d=[scale, scale, scale])
needleColNode.createObject('TriangleCollisionModel', name='instrumentTriangle', contactStiffness=0.1, contactFriction=0.1)
needleColNode.createObject('LineCollisionModel', name='instrumentLine', contactStiffness=0.1, contactFriction=0.1)
needleColNode.createObject('PointCollisionModel', name='instrumentPoint', contactStiffness=0.1, contactFriction=0.1)
needleColNode.createObject('RigidMapping', name='MM-CM mapping', input='@../mechObject', output='@instrumentCollisionState')

# Trajectory
needleNode.createObject('LinearMovementConstraint', template='Rigid3d', indices=0, keyTimes=[0, 0.8, 1.6, 1.7], movements=[[0, 0, 0, 0, 0, 0], [0, -75, 0, 0, 0, 0, [0, 0, 0, 0, 0, 0],[0, 0, 0, 0, 0, 0]]) 

Thanks everyone who can help me,

Cheers,
Luca