Paged.js pushes columns onto the next page when parsing a flexbox based grid system
My use case involves the Salesforce grid (SLDS Grid: https://www.lightningdesignsystem.com/utilities/grid/). You can download SLDS CSS system here: https://www.lightningdesignsystem.com/resources/downloads/
However, any other grid system built on flexbox would have the same issue. Here is a simple example using http://flexboxgrid.com/: flexbox_example.html
Before Paged.js processing:
After Paged.js processing (print modal):
At a higher level, the issue is more about 'side-by-side' content and multiple overflow points. Floats (left/right), use of display: grid, etc would have similar behavior. Whether they can be solved in the same manner is another question.