[Jellby]

I have never tried columns with ADE, but aren't you mixing standard ePub columns (oeb-column-number, which probably doesn't work anywhere) with custom Adobe extensions (page templates, which only work in Adobe-based readers)?

This might help: https://wiki.mobileread.com/wiki/XPGT
or this: https://www.mobileread.com/forums/sho...d.php?t=100625

The page templates do not let you choose the layout mode through CSS, but rather select the layout mode based on, in this case, the screen/window width. Take the template in the latter thread and make it read:

    <fo:page-sequence-master>
        <fo:repeatable-page-master-alternatives>
            <fo:conditional-page-master-reference master-reference="three_column_head" page-position="first" ade:min-page-width="80em"/>
            <fo:conditional-page-master-reference master-reference="three_column" ade:min-page-width="80em"/>
            <fo:conditional-page-master-reference master-reference="two_column_head" page-position="first" ade:min-page-width="50em"/>
            <fo:conditional-page-master-reference master-reference="two_column"/>
        </fo:repeatable-page-master-alternatives>
    </fo:page-sequence-master>

(i.e., remove the single-column option, make two-column the default), and it might work as you want.