Yeah, I am having weird issues too.. I ended up with a file with no background layer (not sure why, is this now expected behavior when opening a new file? ) I created a layer, created background from layer, and somehow the background is now randomly larger than the artboard, and not centered.. and so trying to use the background and an object to align center doesn't work. And even making the layer the correct size, sized to the artboard doesn't work.
Not a fan of the new implementation of artboards.. it appears to be broken, and if I wanted illustrator's tools and behavior, I'd be using illustrator not photoshop..