Game closes to desktop momentarily

Hi all,Have just come back to GW2 for the latest dlc and am experiencing a weird very immersion killing problem and it is infuriating. The problem is I am happily playing along when all of a sudden the game minimises to desktop and then comes back again and plays normally as if nothing has happened. I can find nothing that I think might be causing this running in the background and it appears entirely random. Anyone else experiencing this, any ideas ?

Problem solved. Well a workaround at least. I was playing on full screen (which I omitted to say, sorry). I changed to windowed fullscreen and the problem seems to have gone away. I have no fps loss vis a vis fs. Just for the info I am playing in Win 10 with latest sp and am using 385.41 Nvidea drivers for my 970 .