Do you have the Arbortext variable deepcontentsplitting set to "on"?
In Styler on the Breaks tab for the element wrapping the content under the Keeps, what values do you have for Widows and Orphans? Setting the value determines the minimum number of lines that must be kept at the bottom of the page, widows, and the minimum number of lines that maybe start a page for that element, orphans.
There are also touchup pis that can be added that force a page break or a column break, see Format > Touchup in Arbortext Editor.
One can find documentation about this in Arbortext Editor's Help Center.
Search for widows, orphans and page break.