coremltools: Create MLModel from Spec gives segmentation fault

I have a CoreML Model (Neural Network Classifier) that works well. I want to create updatable model from that one. For this, I wrote the Python script below. But I get zsh: segmentation fault python script.py error when I run script.

import coremltools
from coremltools.models.neural_network.update_optimizer_utils import AdamParams

# File paths:
old_coreml_file_path = 'AModel.mlmodel'
updatable_coreml_file_path = 'updatableAModel.mlmodel'

# Get old CoreML Model:
old_model = coremltools.models.MLModel(old_coreml_file_path)
spec = old_model.get_spec()
builder = coremltools.models.neural_network.NeuralNetworkBuilder(spec=spec)

# CoreML Model to Updatable CoreML Model:
builder.make_updatable(['dense_1', 'dense_2'])

# Set update params:
builder.set_categorical_cross_entropy_loss(name='lossLayer', input='class')

builder.set_adam_optimizer(AdamParams(lr=0.01, batch=8))

builder.set_epochs(allowed_set=[1,2,4,8,16])

# Save Updatable Model:
mlmodel_updatable = coremltools.models.MLModel(spec)
mlmodel_updatable.save(updatable_coreml_file_path)

The error comes in the mlmodel_updatable = coremltools.models.MLModel(spec) line. If I give incorrect input and get a warning in builder.set_epochs section like builder.set_epochs(8, [1,2,4,10,16]), the model is saved without any error, but in my Xcode project, it gives the error about determining the epoch number for the ML Model.

I tried another way to save:

When I try to save with coremltools.utils.save_spec(spec, updatable_coreml_file_path) instead of

mlmodel_updatable = coremltools.models.MLModel(spec)
mlmodel_updatable.save(updatable_coreml_file_path)

at the end of the script, the script runs smoothly, when I drag the saved model to Xcode, MLModel looks good in Xcode and the class is created automatically, but when I build the project, I get the Build Error: Command CoreMLModelCompile failed with a nonzero exit code error. I tried to clean the build folder and rebuild it, but it did’t work.

System environment:

• coremltools version 3.2 (Version 3.0b6 gives same problems.)
• macOS 10.15.3
• XCode 11.3.1
• Python 3.6.8 (anaconda)