I am having the same wifi connection problem after updating to the multi-window update.
After the update, when it was clear it was not working. I did a factory reset....still no connection. At home all my other devices are connected to wifi so I know the network is not the issue.
I than googled it and came across this thread. I have followed the instructions here, restarted the phone, powered off the phone--each time I restarted or powered back on, I made sure the AT&T smart wifi was not enabled. Still no connection.
I'm at a loss. I can't seem to find anyone else having this issue that is not resolved by a factory reset or disabling AT&T Smart wifi.
I'm hoping someone can help!
Thanks so much!