In the hospital waiting room scene where a young girl speaks to Randall McHolland (Christian Stolte), she is wearing a Mettag. By the time she arrived at hospital, both top corners (containing serial numbers) should have been removed by now, as she progressed through the multi-casualty assessment.
When doctors are examining Lexi, there is a large burn on her chest that appears to continue under her clothes, yet her clothes aren't burned. There's no way the skin beneath her clothing could get burned without the clothing also getting burned. Moreover, since only part of her skin is burned, only part of her clothing should be burned as well, yet her clothing looks consistent throughout.
When Suzie, Severide, Casey and the Chief are talking Casey's mike cord outline can be seen through his shirt.
A massive search and rescue effort is made in the burning warehouse. Despite a huge response, not one drop of water is seen being used to put the fire out in any scene.
Several times Alexa Hubble is referred to as Lieutenant, and the character is credited as that rank, yet her collar insignia of two vertical bugles indicates the rank of Captain.