Xcode 6.1 Objects not visible when changing the Canvas Size

I'm very new, so bear with me please.

I've made a new project with Any Sizes for canvas and added some buttons and contained them with Auto layout. Everything worked fine, I tested on an Iphone 6.

But now, if I add for example another button, contained to be in the center of the canvas (horizontal and vertical) I can only see it if I simulate on Adjustable Iphone and Ipad, not the Iphone 6 or any before them.

I've tried to Reset Contents and Settings in the iOS Simulator but the button is not there!

I can see that it is constrained with blue lines in the very center, but when I run it - its gone!

It happened after I built some buttons in AnySize Canvas, and then changed to Horizontal Canvas and back again.

Is there some visual setting or something I've missed? I've managed to successfully align the other elements of the app where I want them, but now if I add something, it doesn't show. Same with ImageViews and Labels.

Please help a n00b out :)