It's not a bug. To be able to play Dijkstra you need to complete 'Broken Flowers' and advance along the 'Get Junior' quest until Sigi will offer Gwent. Note that you *must* beat Dijkstra before completing 'Reason of State'. When you've beaten Dijkstra he will give you the option to play the Scoia’Tael trader.

Thanks for your response. It's a bug that if I was to now play and beat Marquise Serenity, the quest would complete and be over, as far as I can see. When you say "advance along the 'Get Junior' quest" do you mean complete it or simply get it going? I've done everything in that quest up to the point of meeting Roche. All the casino, arena, hideout stuff.

It's not a bug. I have played this game umpteen times and never come across such an issue. If your quest is completing prematurely, either you have reached a stage where Dijkstra is no longer available or you have a mod that's interfering. Or maybe a simple corrupt installation. If you have, for example, passed the point where Dijkstra goes to the Passiflora, he's no longer available -- he must be at his desk in the bath house.

Dijkstra isn't even listed in the quest entry. It says Vivaldi and Marquise Serenity. Vivaldi is ticked, if I beat Serenity, the quest is complete. It's on the wiki as a known bug. It can happen either way around, either you get locked into it just listing VIvaldi and Serenity, but ignoring Dijkstra and the elf, or you get it the other way around. Earlier today I meet Roche and am now at the point where I can meet him in Oxenfurt. I'll do that, finish Get Junior and then go back to Dijkstra and see what happens. He's currently in the bath house - and has been this whole time - so hopefully finishing Get Junior isn't the thing that moves him to the Passiflora. If so, it would be impossible to solve this problem.

EDIT: Yep, finished Get Junior and he still won't play Gwent with me. Here's how it looks (and has always looked) in the quest log (attached pic).