As you say this happened right after you upgraded the software, I advise running a software repair on the handset as this will re-install the software and is quite likely to resolve this issue for you.
To do this you just need access to a computer with an internet connection.
You will need to download either PC Companion or Bridge for Mac.
Note: a software repair will delete all user data, to back
up your phone:
using PC Companion
1. Go to Support to install PC Companion on a Windows
computer.
2. When installed, start PC Companion on the computer.
3. Connect your phone to the computer using a USB cable.
4. Click Start under Backup & Restore.
5. Follow the on-screen instructions.
(Exactly what contents will be backed up may differ
depending on phone model.
You can view detailed information about this as you follow
the steps in the Backup & Restore wizard).
using Bridge for Mac
1. Launch Bridge For MAC.
2. Select "Back up your Xperia device".
3. Select the data you wish to back up from your device
(the windows can be expanded for more detail as below;
then select "Next".
4. The backup will now be in process, do not disconnect
the phone while this runs.
Running the software repair on PC Companion:
1. Install and open PC Companion then select Support Zone.
2. Phone Software Update.
3. Start.
4. Repair Phone
5. Continue
6. Accept data removal
7. Next
8. Wait for prepare
9. Select Phone
10. Follow the connection steps
Running the software repair on Bridge for Mac:
1. Launch Bridge for MAC without the handset connected.
2. On the Main Window select "Xperia > Repair Xperia
Device".
3. Ensure the phone is charged and select "Ok" in the
following window.
4. Select Continue on the following page.
5. Wait until the initialising step is finished the
continue as below.
6 . Select your model of phone from the list that appears
7. Follow the connection steps that appear, ensuring that
you are holding the relevant button down before during and
after the connection phase until the update/repair begins.
Hope this helps, keep us updated