Odd Pages Block issue - duplicated content

[Carl Maltby]

This one is odd purely because of how the issue presents itself. I have a page, "articles" based on template "single_column". In the page builder, the block, "category listings" is added. All is fine. After a bit of use in the wild, the block at some point starts to develop an odd behaviour; duplicating its contents one above the other.

Block working fine...

 

Going back into the page...