[Xperia Z3 Q&A, Help & Troubleshooting] RockStar2005:
I had a similar issue lazi...... the following is what I did which FULLY resolved my issue. Read it carefully:

1) IF AT ANY POINT STAMINA MODE IS NOT WORKING, THEN FOLLOW THESE INSTRUCTIONS: Turn off STAMINA mode. Go into Settings, Apps, All, "Extended Standby Mode Controller", Clear Data AND Cache. Then go to your text app's (Textra, stock, etc….do it for all texting apps you have) "App info" page (on same Apps "All" screen) and clear ONLY the cache, then close out the app itself (3D button to the right of the virtual Home button, swipe the text app(s) off the screen). Reset phone. When you come back, follow #2.

2) Turn STAMINA mode on (under Settings-->Power management), however...... only enable the "Extended Standby" option and of course Activation should be at 100%/Always on. Also make sure “Queue background data” is enabled too. You must also have whitelisted 2 specific apps in STAMINA under the "Apps active in standby" list: The text msg app you're using (i.e. Textra, etc…. the stock app will NOT be listed though) and I would also whitelist one under "All others" entitled "Phone/Messaging Storage". This will allow/ensure that MMS text messages will still come through. Keep the other stuff disabled in Stamina. (You may enable "Stamina Clock" though if you wish. Can't hurt.)

If those don't work, then do #3 then REPEAT #s 1 & 2. Understand though that Sony PC Companion WILL factory reset your phone, and let you update it as well, BUT that people who do both a factory reset and updating via Sony PC Companion (vs not) have more of a tendency to not have issues than those who do not use it. I think for small updates you don't need it, but big ones like Lollipop I would let it do the updating vs OTA.

3) ** Sony PC Companion Instructions:

We have an extended guide that should help you fix the issue on your phone, please follow the instructions carefully:

Visit this link:

http://www.sonymobile.com/us/tools/pc-companion/

Click on Download PC Companion

Run the software and install it

Turn the phone off and disconnect it from the computer

1. No matter what the program says do not connect the phone until you complete step 9

2. In the welcome screen you will see the different modules available for you including the "Support Zone" option. Click on "Start" below it.

3. On the next page Click on "Start" under "Phone Software Update"

At this point if you get an error stating that "Unable to install update components" or "Server is busy" , then please proceed to step 12

4. The program will say that there is no phone connected. Click on the option below that reads: "Repair my phone" the program will issue you a warning about the content that you will lose during the update

5. Choose the option to continue.

6. The program will issue a final message warning you of possible data lost during the update. Click on the checkmark and then on "Next".

7. After that, the program will download the necessary information (5 to 6 minutes) and it will present you with a list of phones.

8. Choose your phones model from the list then click on "Next" then you will see a new section telling you how to connect the phone. (don't connect it yet) (YOU CAN FIND YOUR PHONE’S MODEL # BY DOING THIS: SETTINGS->ABOUT PHONE->MODEL NUMBER)

At this point the phone must be off and disconnected from the PC.

9. Connect the cable to the PC not to the phone, then while pressing and holding the indicated button (in the steps on screen an specific button will be shown for you to press on the phone) connect the cable to the phone and keep holding the indicated button until the program says "the update of your phone has started..." (in some cases a message of "Installing drivers" will appear before the message of "the update of your phone has started..." is shown.)

10. If you failed to follow the steps correctly the phone will turn on and it will request that you "Proceed with the following steps, slide down the notification bar", If this happens disconnect the phone from the cable, turn it off and repeat from step 9).

11. If the phone is connected properly, PC Companion will proceed with the update (It will tell you to let go of the back key) then wait for the update to finish and follow instructions on screen to disconnect the unit.

Dear Customer,

12. If "Unable to install update components"

1. Close PC Companion

2. Install Java from: http://www.java.com

3. Start PC Companion again and try to do the software unlock process once more.

Note: If you wish only to update the unit wait for the program to open and then select the quick link on the upper left corner that says "Update Phone/Tablet" and follow the instructions to perform the update. (the PC may request for the phone to be placed in Mass Storage mode. Do this by going into Settings>Xperia>Connectivity>USB connection mode)﻿

RockStar2005