After long time I decided to play the campaign again and get all missing achievements. I have all achievements except Dominion Tech Master. I played the Wings of liberty campaign several times, I’m really sure I had all 4 dominion upgrades in one game, both combinations (ghost + thor and spectre + thor), but it is still missing… Last time I played the campaign on casual difficulty to finish it quickly, can this be the issue? There is no difficulty level limitation in the achievement description.
You might have had problem with connection when you paid for the tech.
Casual shouldn’t be a problem.