In this minimal example, the width of the first column is set correctly in the browser based on either the width or the min-width property set on the first col in a colgroup. When converted to a PDF with Prince 15, only the width property has an effect.
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Cannot use min-width in colgroup to set the width of a table column
I figured out that it's not just col elements in colgroup that are not affected by the min-width property, but also cells (td and th elements) See attached example.