Can't write to a serial port twice using Pyserial without closing and reopening the port in between writing data

Question

If I open a port with Pyserial then try to write GCode to a printer controller board twice, the second command does not execute. If I close the port after the first time data is written, then reopen it and write again, it works fine. I have found another stackoverflow post detailing the same problem, but the solution does not apply to my code because the serial object instantiation defaults to dsrdtr=False. Here is my code:

from serial import Serial
from typing import cast
import time

serial = Serial(str('COM4'), 115200, timeout=2, writeTimeout=3) # Open port

time.sleep(1) # Wait for board to boot
serial.write(b'G00 X25\n') # Rotate stepper motor

time.sleep(2) # Wait 2 seconds or else the port will close before the motor stops rotating

serial.close()
serial.open()

time.sleep(1) # Wait for board to boot
serial.write(b'G00 X25\n') # Rotate stepper motor

What could explain this behavior?

Answer 1

Solved: Problem was unrelated to software. Figured out that the endstops of my board were always triggered by using serial.write(b'M119\n'). Fixed by connecting the endstop in the normally closed configuration.