UICollectionViewCell content wrong size on first load
It looks like it still retains it's 100x100px basic size for the contentView while the cell itself gets the right size already. You can force the layout to reset adding the following line just before you return the cell:
cell?.layoutIfNeeded()
What worked for me was changing Estimate Size on the Collection View from Automatic to None.
I had once similar problem (content of my cell was not fitting cell even with correct autolayout). The bug was caused by not calling super.layoutSubviews() in overriden function layoutSubviews() that was in Cell's class.