Achievement weirdness

I've had a couple of games lately where my achievements have arrived all at the same time, and haven't been displaying when they should have been achieved - Agarta (which I may have unfairly slandered) and Pendula Swing (and before that the non-SG Jedi Fallen Order, although I'd had a lot of play before that, and put it down for ages, so I don't know if that's related). In the case of Pendula Swing, they showed up when I quit. I don't use any achievement-related software. I do tend to play Invisible rather than Online (but not Offline), but don't see why that should be the cause given it's not every game -- Dorf Romantik and Hellpoint and a bunch of others look fine. Any ideas?