I can’t reply more than 3 times – so disregard this recommendation. Our sites now execute masonry grid with the Colcade library.
ok, circling back on this →
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Make sure to set your collection list “layout” option to full width

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Set your collection list to flex with the below settings:

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Give your collection list item a width of 100/3%:

If this doesn’t work, then I’d suggest use a new javascript masonry grid.