VideoWriter result in a corrupted video when its set on 2fps

I am trying to read a video, crop each frame from top and bottom and then write back each frame and also write them in to a video in mp4 format. The input video is at 2fps and it is also in mp4 format. The frames are saving properly but I can not write them as a 2fps video. I have tried other frame rates such as 1fps, 3fps, 5fps, 10fps and even 25fps. All of them work properly except 2fps, which result in a corrupted video (either its not showing any fame except the fist frame, or its just displaying a green screen) Any thoughts or comments will be appreciated:

reader = cv2.VideoCapture('video.mp4') 
cropped_video = os.path.join('video_crop.mp4')
cropped_frames = os.path.join('video/')

if (reader.isOpened() == False):
    print('Error while trying to open video. Plese check again...')
else:   
    # get the frame width and height
    frame_width = int(reader.get(cv2.CAP_PROP_FRAME_WIDTH ))
    frame_height = int(reader.get(cv2.CAP_PROP_FRAME_HEIGHT))
    frame_count = int(reader.get(7))
    fps =  int(reader.get(cv2.CAP_PROP_FPS))
    print('frame_width, frame_height, frame_count, fps = ', frame_width, frame_height, frame_count, fps)

    # define codec and create VideoWriter object
    fourcc= cv2.VideoWriter_fourcc(*'XVID')#*"MP4V")
    writer = cv2.VideoWriter(cropped_video , fourcc, 2, (frame_width, frame_height))

top = 20
botton= frame_height-20

count = 0

# read until end of video
while True:
    ret, frame = reader.read()
    if ret==True:
        cropped = frame[top:botton , :]
        frame = cv2.resize(cropped, (frame_width, frame_height), interpolation = cv2.INTER_NEAREST_EXACT) 
        # save video frame
        cv2.imwrite(os.path.join(cropped_frames,"frame%d.jpg" % count), frame)
        writer.write(frame)
        count += 1
        print(count)
    else:
        break

            

# release VideoCapture()
reader.release()
writer.release()
# close all frames and video windows
cv2.destroyAllWindows()