I've got somewhat of a fix for this.
My last two iMacs have done it regularly when waking from sleep, neither running Spotify, and my old one never had Creative Cloud so it shouldn't be related to those. For me it's been happening since Yosemite, and whatever OS came before that, on the Slim iMacs.
To "fix" this, I've noticed that swiping across the Magic Trackpad (3 fingers) to switch desktops brings the display back up temporarily. When I let go, it will go black again. This usually happens a few times, but suddenly it will bring the display back properly after 3-4 attempts swiping left and right.
It's very irritating, but if you have multiple desktop spaces and a magic trackpad, with a couple of swipes it can be fixed.
Hoping Apple sorts this out properly soon.