Hi Ciaran
there is an issue for the «Category Blog» layout on mobile screens. Let's assume the setting is «# Columns» = 2. On a mobile screen the two columns are displayed although there is not enough space for displaying two columns correctly. The second column extends beyond the edge of the screen.
By the way: when I use «Category Blog - Masonry» it works. I have never seen «Category Blog - Masonry» in Joomla websites before. This seems to be a special feature provided by the Nina template.
Thank you and kind regards
Chris