Kivy GUI freezes when calling another framework

Question

I try to call pandasgui after pressing a button and choosing a file using kivy framework, the process works fine and pandasgui behave in a normal manner but when i try to comeback to kivy it freezes and i should restart the app,I was being told that i should use threading but i'm still not sure how to proceed , any ideas ?

function call when button clicked :

import kivy
from pandasgui import show

# this restrict the kivy version i.e
# below this kivy version you cannot
# use the app or software
kivy.require("1.9.1")

# base Class of your App inherits from the App class.
# app:always refers to the instance of your application
from kivy.app import App

# creates the button in kivy
# if not imported shows the error
from kivy.uix.button import Button


# class in which we are creating the button
class ButtonApp(App):

    def build(self):
        # use a (r, g, b, a) tuple
        btn = Button(text="Push Me !",
                     font_size="20sp",
                     background_color=(1, 1, 1, 1),
                     color=(1, 1, 1, 1),
                     size=(32, 32),
                     size_hint=(.2, .2),
                     pos=(300, 250))

        # bind() use to bind the button to function callback
        btn.bind(on_press=self.callback)
        return btn

    # callback function tells when button pressed
    def callback(self, event):
        import pandas as pd
        import pickle
        from sklearn.metrics import confusion_matrix, ConfusionMatrixDisplay

        data_test = pd.read_csv('test_data.csv')
        # Extract test labels from data_test
        y_test = data_test['target']
        # Extract test data
        X_test = data_test.iloc[:, 1:-1]
        # Load pre-trained data
        loaded_model = pickle.load(open(r'GVHD.sav', 'rb'))
        # Predict labels
        y_pred = loaded_model.predict(X_test)

        # disp.figure_.savefig(r'C:\Users\44755\Downloads\confusion_matrix.jpg')

        # Concatenate all test data
        from matplotlib import pyplot as plt

        new_data = pd.concat([X_test, y_test, pd.DataFrame(y_pred, columns=['Predicted response'])], axis=1)
        # Save output
        new_data.to_csv(r'GVHD_Output_data.csv', index=False)
        # Create confusion matrix
        disp = ConfusionMatrixDisplay(confusion_matrix=confusion_matrix(y_test,
                                                                        y_pred,
                                                                        labels=[0, 1],
                                                                        normalize='true'),
                                      display_labels=['low risk', 'high risk'])
        disp = disp.plot(cmap=plt.cm.Blues)
        # Save confusion matrix
        disp.figure_.savefig('confusion_matrix_GVHD.jpg')

        df = pd.read_csv('GVHD_Output_data.csv')
        show(df)


# creating the object root for ButtonApp() class
root = ButtonApp()
root.run()