UIKits API for registering UINibs to UICollectionViews looks bad. Just look at this.
sizeCollectionView.register(UINib(nibName: "SearchFilterSizeCell", bundle: nil), forCellWithReuseIdentifier: "sizeCell")Using them again is even worse;
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "sizeCell", for: indexPath) as! SearchFilterSizeCell