I added music to my iPhone through my computer, realized I forgot to add cover art, deleted the music from my phone, added the cover art, but now I can’t re-add the music because iTunes on my computer says it’s all still on my phone (now with an exclamation mark!), despite the phone music app disagreeing.
EDIT: Music works now, but cover art still doesn’t show up on the phone. Hm… This probably shouldn’t bother me as much as it does.