cap = cv2.VideoCapture(video_path)
cap.get(cv2.CAP_PROP_FRAME_COUNT)
gives 172 frames. And while counting manual:
while(cap.isOpened()):
        ret, frame = cap.read()
        if ret == True:
            frame_index += 1
        else: 
            break
it can't go any further than 168 frame
Sadly I can't share the video file
env: OPENCV_VIDEOIO_DEBUG=1
env: OPENCV_FFMPEG_DEBUG=1
extract frames from your video using FFmpeg and compare with OpenCV output (you may read extracted frames images through imread()): https://stackoverflow.com/questions/10957412/fastest-way-to-extract-frames-using-ffmpeg
dump frames information and analyse them: https://stackoverflow.com/questions/27529930/get-video-frames-information-with-ffmpeg
We don't help with remote investigation of problems which we are not able to reproduce on our side (because it is very time consuming), but we can take a look on the clear reason of the problem and suggest some fix/workaround.
          
@alalek : I talked to my colleagues again and we decided to upload the video after all

video.zip
I hope this will bring some clarity for the problem
Video stream is 1:
  Duration: 00:00:06.93, start: 0.000000, bitrate: 26676 kb/s
    Stream #0:0(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 317 kb/s (default)
    Metadata:
      creation_time   : 2020-04-27T07:51:47.000000Z
      handler_name    : #Mainconcept MP4 Sound Media Handler
    Stream #0:1(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080, 26491 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2020-04-27T07:51:47.000000Z
      handler_name    : ?Mainconcept Video Media Handler
      encoder         : AVC Coding
OpenCV stops decoding after 168 frame.

Problem is that frames are not flushed from the decoder properly after the stream EOF (passed stream index 0 instead of 1).
PR with fix will be added soon.