item_group_id does the grouping
Without it, every size and colour is a separate product competing in the same auction. You bid against yourself and split conversion data across two dozen entries.
Size and colour belong in the title
Because that is how people search. "Black midi dress, size 12" matches; "SS26 Collection Dress — SKU 4471" does not.
What else breaks fashion feeds
- Images with promotional overlays burnt in.
- Prices that drift when a sale app rewrites them client-side.
- Availability that does not sync fast enough during a drop.
More: the fashion vertical and feed optimisation.