Basic to everyone but Arteta.
It's so confusing. Instead of bringing on the backup CB you proceed to end up weaken 4 positions by putting Timber at CB when he's better at RB, putting Partey at RB when he's better at 6, putting Rice at 6 when he's better at 8 (though some will debate this so ok ignore this one if you want), and putting Merino at 8 when he's better on the bench.