I've noticed that with some devices. Mostly Android. It scales up great, but a few refuse to scale down. (not all Android)
I've take to making the games smaller, usually 800x450. (16x9)
It's the full size graphics scaled down, so when displayed at 1920x1080 they appear full quality.
Plus since the games are smaller than 800, they can be uploaded to the Scirra arcade.
After it's already built however, can be difficult. I re-scaled 3 games like that, some more difficult than others.
Someone was working on a scaling Program to assist doing a lot of it for you, but I lost track of that thread.