Are you running the latest version?

You may also try saving and reloading the game to see if that shakes the button loose.

Green turn button is not the same as a disappearing turn button.

Disappearing turn buttons are caused by something (generally the AI moving ships) not happening when its supposed to, so the turn is never finished and the button doesn't reappear. This issue has been around in one form or another pretty much forever (back into the beta). Every time the devs squash it, it still seems to come back for at least one or two people under certain circumstances.

The turn button staying green/not turning green is related to [user-requested] changes made to how unmoved ships are handled in 1.2/1.3, IIRC. I'm not a dev, so I can't say as to why it would not affect everyone.

I've had the Turn button dissapear before. I don't recall exactly, but I think it was because I was trying to make a ship do something it's not supposed to do, like a transport with no weapons trying to invade a defended planet. I've fixed it by either correcting the condition or restarting the game from the last save.

Well, it looks like a legit problem, then. It stink, though, because it only seems to happen when I am playing on a huge honkin map!

I’ve had a number of different turn button disappearances in the last beta of DA, also in DL and the previous DA beta.
What I haven noticed however is that there is a movement icon in the bottom left corner of my screen, way at the end of the map. It’s a destination without an ETA. It almost looks like a ship is trying to move of the edge of the map. Thus far it has only happened mid game in gigantic galaxies. When I generally have a lot of ships flying around and I haven’t had the patience to see which one is trying to get of the map. I will see if I have a safe game with this bug.

Disappearing turn buttons are caused by something (generally the AI moving ships) not happening when its supposed to, so the turn is never finished and the button doesn't reappear. This issue has been around in one form or another pretty much forever (back into the beta). Every time the devs squash it, it still seems to come back for at least one or two people under certain circumstances.

I just had this happen to me in a game (turn button disappeared). Re-loading a save did not work, but exiting the whole game and then restarting the game did solve the problem. This was the first time this has ever happened to me.

This also happened to me in the current version 1.4x of the game. Hopefully can reload from a previos save. Reloading from autosave worked once before.