Each and every one of those is an Apple Mobile device which refused to disassociate from one AP and associate with another, closer AP when its user walked from one room to another. TX is low on all APs. All APs have a very robust minRSSI set. iDevices are the *only* devices I've ever seen refusing to roam like this. Everything else on site, from IoT garbage through Android phones to laptops and more, roams freely and easily as their users do.