Long story short i have been to a friends house. He has 119 gog games i know because he kinda brags about them.
When he logged in i dont know exactly it was back 2 weeks from today, the library had 120, he was like wtf ? i didnt bought anything.
He was tired and said there must some game added as a bonus or something. The next day he checked again and called me saying : Dude still 119 ? What was that the mysterious 120 game added we should have definitely check it yesterday.

Anyone encounter this bug ? Does a game from library could have caused the bug and a duplicate of it popped out ?
Mystery gog game... what was it ? He still wonders.

Hmmm... were not for the total count going back to 119 I would've said the increase was due to some unbundling (the most recent one being the Sword of the Stars one, I think), but in this case I'm not so sure...

Can you detail a little bit what unbundling ? As i said he didnt purchased anything in that week.
Forgot to mention he has all the free games on site added too, i did mention to him : Hey maybe its the Metro Mini tba bug..

I will ask about the game title you mention to see if he has that one too.

If your friend had The Witcher 3 then 120th game was The Witcher 3 Arabic version.

there : http://hastebin.com/raw/wupocefuwu

he should try an account reshesh (CTRL + R) first.

also a list of the games could help, whithout knowing which ones are on the account, we are almost clueless.

Is that for real? Why is it considered a different library entry than the regular W3? GOG used to sell some old games "bundled" together because otherwise nobody would buy them separately (since, if I'm not wrong, originally games on GOG were either $6 or $10 only). E.g. you could buy Silent Service and Silent Service II together, and they appeared as a single library entry.
For some reason, at some point they decided to unbundle many of those games so every game in the former bundle now counted as a single library entry. Hence, your total game count could go up even though you hadn't bought anything recently.

I don't know.
But when I went to TW3 ARABIC game page it was written TBA.
May be it was one of the testing of recent TW3 1.10 patch or may be soon Gog is going to support arabic.

There was a transitory bug on October 2nd, whereby some of the DLCs of Sword of the Stars The Pit appeared as separate boxes on people's shelves, resulting in game counts increasing for a day or so by anywhere between +1 and +4.

there was The wither 3 bug aswell (IIRC), but the timeframe doesn't match , unless the OP mistaken about it....