Was told by AT&T tech (at store) that the IOS 12.5.4 download had a security element in it that rendered my older I-Pad unable to enter or change a password in order to use "Yahoo Mail" . Same thing happened to my I-Phone 6 when I downloaded the same version. Wound up having to purchase a new I-Phone (not a new one, but I-Phone 7). Don't want to buy a new I-Pad! Still having to pay "access fees", on it though. Texting, calling, and Facetime work OK, but not E-Mail....