Question regarding the quality of “JoyBell” releases (stuttering issue)

Hi,

Yesterday I downloaded the movie “Django unchained”, from a torrent tagged as such :
Django Unchained (2012) [1080p x265 q18 FS100 Joy] (size = 5.22GB)
I had formerly watched other movies / episodes from the same source and was pleased with the quality / size ratio, as well as the wealth of embedded subtitles (this one has no less than 40 subtitle streams — I'll only ever need english and french but that doesn't hurt, and it demonstrates the creator's dedication to please everyone).

Then I started watching the movie, and quickly noticed a disturbing issue: there's a brief stuttering every once in a while, with no obvious pattern; as I examined it more carefully I could see, in each instance, two duplicated frames followed by the frame normally present at n+2, meaning that the frame n+1 is absent, producing that stuttering effect, particularly noticeable on shots with rapid motion.
To rule out a possible glitch introduced by VLC Media Player, I examined it with SMPlayer, and it exhibited the exact same issue at the exact same timecodes.

Now what could have caused this ? Is it a known issue which affected x265 at some point ? Or is it due to a specific setting that was used to create that encode ? Or could it be a computer related issue ? Has anyone noticed that kind of issue, on JoyBell's releases or others ?

If someone has that same file and cares to verify, here are timecodes I noted at which that stuttering can be observed:
00:15:56
00:47:25
00:53:26
00:57:30
01:00:54
01:02:35
01:03:30
01:04:51
01:05:22
01:05:30
01:08:21
01:09:22
01:10:15
Both VLC Media Player and SMPlayer allow to read a video frame by frame, so it's quite easy to check. It should be possible to detect them all with an Avisynth script, in order to check if there is a pattern or not, and in order to automatically check other files.

I did a Web search with keywords « unity team joybell » and this was among the first hits.

Thanks.

EDIT : Also, if someone is in touch with “JoyBell” or anyone from the UTR team, would you please link this post to them ?

EDIT : Forgot to mention, I first tried the uniteam.co forum, following the link posted in the aformentioned thread, but it seems to be dead.