Raspberry freezes when closing serial connection

Question

I wrote a Python script with pyserial to read data from two different USB devices (Witmotion IMU, Ublox ZED-F9P GNSS Receiver). This works perfectly on Windows. Every time I run the same script on a Raspberry Pi 4B (fresh Raspberry Pi OS) the whole Raspberry just freezes/crashes when trying to close the connection. So I can get data from the serial port and do whatever I want with it as long as I don't close the connection. Am I doing something wrong?

This is a minimal "working" example with that I can reproduce the crashes on any Raspberry 4B I have (tried it on 3 Raspberrys and on a VM running Raspberry Pi OS):

import threading
import serial
import time

def loop():
    ser = serial.Serial(port='/dev/ttyUSB0', baudrate=115200)
    while run_event.is_set():
        print("connected")
    ser.close() # freeze
    print("disconnected")

run_event = threading.Event()
run_event.set()
t = threading.Thread(target=loop)
t.setDaemon(True)
t.start()

time.sleep(10)

run_event.clear()

(Edit: Btw I get the same result if I do this without threading with some timer or limited number of loops:

import threading
import serial
import time

ser = serial.Serial(port='/dev/ttyUSB0', baudrate=115200)
while i < 10:
    print("connected")
    time.sleep(1)
    i = i+1
ser.close() # freeze
print("disconnected")

Note that it does only crash after stopping the connection. It also crashes when I just try to close the command line window while it still prints "connected".

I also noticed that I can make the Raspberry crash with the following command:

stty -F /dev/ttyUSB0 115200 -echo > /dev/null

Does anyone have some ideas on how to get the USB devices closed properly?