Pyqt threaded processes application crashing on second launch - python-3.x

Question

I made a small test application to practice threading - on the first launch it works fine, with the loop printing to the console while the gui is still running. However, the kernel crashes and restarts if I close the app and then open it again afterwards.
I've had this issue before with pyqt5 applications, and it's usually solved when I add the QCoreApplication.instance() section at the end of my script. I was wondering whether this time there was an error with the way I implemented my threading.
import sys
import time
from PyQt5 import QtWidgets
from PyQt5.QtCore import QObject, QThread, pyqtSignal
from PyQt5.QtCore import QCoreApplication
class Worker(QObject):
finished = pyqtSignal()
def __init__(self):
super(Worker, self).__init__()
self.working = True
def work(self):
while self.working:
# do stuff here
print("I'm running")
time.sleep(1)
self.finished.emit() # alert our gui that the loop stopped
class Window(QtWidgets.QMainWindow):
def __init__(self):
super(Window, self).__init__()
self.setGeometry(50, 50, 200, 150)
self.setWindowTitle("Program")
self.startbtn = QtWidgets.QPushButton("Start", self)
self.startbtn.resize(self.startbtn.minimumSizeHint())
self.startbtn.move(50, 50)
self.stopbtn = QtWidgets.QPushButton("Stop", self)
self.stopbtn.move(50, 100)
self.stopbtn.resize(self.stopbtn.minimumSizeHint())
self.thread = QThread()
self.worker = Worker()
self.worker.moveToThread(self.thread)
self.startbtn.clicked.connect(self.thread.start) # start the thread when we click the start button
self.thread.started.connect(self.worker.work) # begin our worker object's loop
self.stopbtn.clicked.connect(self.stop_loop) # stop the loop on the stop button click
self.worker.finished.connect(self.loop_finished) # do something in the gui when the worker loop ends
def stop_loop(self):
self.worker.working = False
def loop_finished(self):
print('Looped Finished')
if __name__ == "__main__":
app = QCoreApplication.instance() # Fixes error with kernel crashing on second run of application
if app is None: # PyQt doesn't like multiple QApplications in the same process, therefore
app = QtWidgets.QApplication(sys.argv) # apart from the initial run, the first QApplication instance will run
window = Window()
window.show()
app.exec_()