Hey Karen,
I already consult with our developer regarding this, actually that is correct behaviour the way we use
masonry library Javascript to populate column layout in Nickel theme, you can refer on this link (
https://medium.com/@andybarefoot/a-masonry-style-layout-using-css-grid-8c663d355ebb ) (Copy this whole link)
So that Javascript according the shortest column height then display the column first on the page, you can check my screenshot here for further explanation :
http://take.ms/ZcSJ1
If you would like to display the 3 columns for your blog listing page, perhaps you can consider to switch the blog menu type to Grid layout, so it will show 3 columns as well. ->
http://www.accesstalent.co.uk/testgridblog