[Xperia Z3 Q&A, Help & Troubleshooting] SheepWind:
Thanks, really good info, but I'm not sure it will work. Flashtool is saying USB debugging has to be enabled (which it isn't in my case). I'm pretty sure unknown sources is enabled.

Here's the log from Flashtool when I exclude everything but cache.

01/015/2017 09:15:35 - INFO - Device connected in fastboot mode
01/015/2017 09:15:36 - INFO - Device disconnected
01/015/2017 09:15:48 - INFO - Device connected with USB debugging off
01/015/2017 09:15:48 - INFO - For 2011 devices line, be sure you are not in MTP mode
01/016/2017 09:16:09 - INFO - Device disconnected
01/016/2017 09:16:13 - INFO - Flash canceled
01/016/2017 09:16:22 - INFO - Device connected in fastboot mode
01/018/2017 09:18:59 - INFO - Selected Bundle for Sony Xperia Z3(D6653). FW release : 23.0.A.2.93. Customization : Customized IN
01/018/2017 09:18:59 - INFO - Preparing files for flashing
01/018/2017 09:18:59 - INFO - Please connect your device into flashmode.
01/019/2017 09:19:06 - INFO - Device disconnected
01/019/2017 09:19:13 - INFO - Device connected in flash mode
01/019/2017 09:19:14 - INFO - Opening device for R/W
01/019/2017 09:19:14 - INFO - Device ready for R/W.
01/019/2017 09:19:14 - INFO - Reading device information
01/019/2017 09:19:14 - INFO - Phone ready for flashmode operations.
01/019/2017 09:19:14 - INFO - Opening TA partition 2
01/019/2017 09:19:14 - INFO - Current device : D6653 - CB5A248496 - 1288-4247_R5C - 1282-2729_23.4.A.1.232 - APAC-LTE_23.4.A.1.232
01/019/2017 09:19:14 - INFO - Closing TA partition
01/019/2017 09:19:14 - INFO - Start Flashing
01/019/2017 09:19:14 - INFO - Processing loader.sin
01/019/2017 09:19:14 - INFO - Checking header
01/019/2017 09:19:14 - INFO - Flashing data
01/019/2017 09:19:15 - INFO - Loader : S1_Root_9c84 - Version : MSM8974AB_22 / Boot version : S1_Boot_MSM8974AC_LA3.0_52-2 / Bootloader status : ROOTABLE
01/019/2017 09:19:15 - INFO - Max packet size set to 512K
01/019/2017 09:19:15 - INFO - USB buffer size set to 512K
01/019/2017 09:19:15 - INFO - No flash script found. Using 0.9.18 flash engine
01/019/2017 09:19:15 - INFO - Opening TA partition 2
01/019/2017 09:19:15 - INFO - Writing TA unit 00002774. Value : 01
01/019/2017 09:19:15 - INFO - Closing TA partition
01/019/2017 09:19:15 - INFO - Opening TA partition 2
01/019/2017 09:19:15 - INFO - Closing TA partition
01/019/2017 09:19:15 - INFO - Opening TA partition 2
01/019/2017 09:19:16 - INFO - Processing cache.sin
01/019/2017 09:19:16 - INFO - Checking header
01/019/2017 09:19:16 - INFO - Flashing data
01/019/2017 09:19:17 - INFO - Closing TA partition
01/019/2017 09:19:17 - INFO - Opening TA partition 2
01/019/2017 09:19:17 - INFO - Closing TA partition
01/019/2017 09:19:17 - INFO - Opening TA partition 2
01/019/2017 09:19:17 - INFO - Closing TA partition
01/019/2017 09:19:17 - INFO - Opening TA partition 2
01/019/2017 09:19:17 - INFO - Closing TA partition
01/019/2017 09:19:17 - INFO - Opening TA partition 2
01/019/2017 09:19:17 - INFO - Writing TA unit 00002725. Value : 32 30 31 37 2D 30 36 2D 30 31 20 30 39 3A 31 39 3A 31 37 00
01/019/2017 09:19:17 - INFO - Writing TA unit 00002774. Value : 00
01/019/2017 09:19:17 - INFO - Closing TA partition
01/019/2017 09:19:17 - INFO - Ending flash session
01/019/2017 09:19:17 - INFO - Flashing finished.
01/019/2017 09:19:17 - INFO - Please unplug and start your phone
01/019/2017 09:19:17 - INFO - For flashtool, Unknown Sources and Debugging must be checked in phone settings
01/019/2017 09:19:17 - INFO - Device connected in flash mode