This is after the storyline with yennifer, where you steal the mask and use it in the forest.
The symbol is on the map for him below the druid camp, but nothing is there, cept some animals and a monster or two. :-s

Bug or no?

I believe is not a bug. From the beginning ver 1.0 there was no merchant. I could clearly see a mark on a map but there was no merchant 'open for business'.

Thing is, when the game first came out, I did see a merchant there; he just wouldn't talk to me
He was also missing after I completed the storyline quest in that area.

I'm pretty sure you need to play gwent with that guy to get the all cards thing, so it bothers me that he's missing.
Also if he's removed for storyline reasons, then the marker on the map should disapear too.

UR right about gwent, but that's not the same guy. Just finish the mission and when Yen depart, u follow Ermion and start talking with him. U should get an option to play gwent with Ermion, That's the guy u need.
PS
Just couple days ago I have done exactly the same ( playing this game at least 6th time )

Well... I did get ermions and the others that have quests.
However when I played through at release, I explored every nook and cranny of the maps and stil didn't get the gwent card achievement; it bugs me.

That's the only merchant I never found and played, to my knowledge. :-s

I had the same problem. I think I've got this achievement during 3th time I played the game. But I thing I didn't play this guy u looking for.

hmmmm
Well I'll keep pluggin away at it and see if I get the achievement without it this time.