Grouped Shapes / Outlines (Almost) Disappear After Creating Pattern?

I’ve selected a bunch of shapes and outlines for a pattern. I’ve gone to Object > Group, to group them all together, dragged them to the swatches panel to create a new swatch, and then after double-clicking that swatch, it brings up the Pattern Options panel. After approving the settings and clicking ‘Done’, the pattern is completely ruined, with most of the shapes reduced to a couple lines or nothing at all: