Bootstrap Theme: Not working on mobile devices
On every mobile device the size of the screen-width seems fixed to 980 pixels and I don't know why.
it seems you forgot to add this line in the header of your concrete5 theme:
<meta name="viewport" content="width=device-width, initial-scale=1">
Try adding that line and see if that fixes it.
I was totally convinced that Concrete5 would fill in the viewport-code. Sometimes you don't see the forest for the trees.