Share your experience!
I am using a Plantronics Voyager Legend bluetooth with my Xperia Z Ultra. The call gets disconnected frequently. I am able to talk for a few seconds and then it gets disconnected without a warning or anything even when i am wearing bluetooth device with the phone beside me.
I have tried multiple times to go and manually connect to the bluetooth device. It works sometimes and sometimes it just says connection failed.
Wired headsets do not have any problem. It is only with the bluetooth headset.
I havent tried with any other bluetooth headset.
Make sure that you have the latest software on your Xperia Z Ultra:
www.sonymobile.com/global-en/tools/pc-companion/
You can also check so Wi-Fi is not activated under Settings > Wi-Fi. But if the problem persist, I suggest that you try with another Bluetooth-headset. Preferably a Sony headset to see if the problem is in your phone or if it's a compatibility problem and/or a problem with the headset itself.
Exactly the same problem with my Xperia Z1 Compact. Sony support suggested me to buy a sony headset!
Try to connect using the "throw" option. This worked for me.