[XDA Assist] huntedman:
So tried flashing another ROM today, didn't get the weird error anymore. But the phone is still not turning on. It's just showing me the sony xperia logo and restarts.

The log from flashtool:

16/035/2016 11:35:44 - INFO - Device connected in flash mode

16/036/2016 11:36:04 - INFO - Selected Bundle for Sony Xperia ZL(C6503). FW release : 10.6.A.0.454_R1E. Customization : Nordic Generic_1270-6779

16/036/2016 11:36:04 - INFO - Preparing files for flashing

16/036/2016 11:36:19 - INFO - Please connect your device into flashmode.

16/036/2016 11:36:20 - INFO - Opening device for R/W

16/036/2016 11:36:20 - INFO - Device ready for R/W.

16/036/2016 11:36:20 - INFO - Reading device information

16/036/2016 11:36:20 - INFO - Phone ready for flashmode operations.

16/036/2016 11:36:20 - INFO - Opening TA partition 2

16/036/2016 11:36:20 - INFO - Current device : Unknown: Apr 27 2015/08:46:48 - EP7305027H - Unknown: Apr 27 2015/08:46:48 - Unknown: Apr 27 2015/08:46:48 - Unknown: Apr 27 2015/08:46:48

16/036/2016 11:36:20 - INFO - Closing TA partition

16/036/2016 11:36:20 - INFO - Start Flashing

16/036/2016 11:36:20 - INFO - Processing loader.sin

16/036/2016 11:36:20 - INFO - Checking header

16/036/2016 11:36:20 - INFO - Flashing data

16/036/2016 11:36:21 - INFO - Loader : S1_Root_5ca3 - Version : APQ8064_39 / Boot version : S1_Boot_Lagan_1.1_10 / Bootloader status : ROOTED

16/036/2016 11:36:21 - INFO - Max packet size set to 512K

16/036/2016 11:36:21 - INFO - USB buffer size set to 512K

16/036/2016 11:36:22 - INFO - Parsing boot delivery

16/036/2016 11:36:22 - INFO - No flash script found. Using 0.9.18 flash engine

16/036/2016 11:36:22 - INFO - Opening TA partition 2

16/036/2016 11:36:22 - INFO - Writing TA unit 00002774. Value : 01

16/036/2016 11:36:22 - INFO - Closing TA partition

16/036/2016 11:36:22 - INFO - Processing partition-image.sin

16/036/2016 11:36:22 - INFO - Checking header

16/036/2016 11:36:22 - INFO - Flashing data

16/036/2016 11:36:22 - INFO - Phone boot version : S1_Boot_Lagan_1.1_10. Boot delivery version : S1_Boot_Lagan_1.1_10

16/036/2016 11:36:22 - INFO - Boot delivery up to date. Nothing to do

16/036/2016 11:36:22 - INFO - Opening TA partition 2

16/036/2016 11:36:22 - INFO - Closing TA partition

16/036/2016 11:36:22 - INFO - Opening TA partition 2

16/036/2016 11:36:22 - INFO - Processing amss_fs_1.sin

16/036/2016 11:36:22 - INFO - Checking header

16/036/2016 11:36:22 - INFO - Flashing data

16/036/2016 11:36:22 - INFO - Processing amss_fs_2.sin

16/036/2016 11:36:22 - INFO - Checking header

16/036/2016 11:36:22 - INFO - Flashing data

16/036/2016 11:36:22 - INFO - Processing amss_fs_3.sin

16/036/2016 11:36:22 - INFO - Checking header

16/036/2016 11:36:22 - INFO - Flashing data

16/036/2016 11:36:22 - INFO - Processing cache.sin

16/036/2016 11:36:22 - INFO - Checking header

16/036/2016 11:36:22 - INFO - Flashing data

16/036/2016 11:36:24 - INFO - Processing fotakernel.sin

16/036/2016 11:36:24 - INFO - Checking header

16/036/2016 11:36:24 - INFO - Flashing data

16/036/2016 11:36:25 - INFO - Processing kernel.sin

16/036/2016 11:36:25 - INFO - Checking header

16/036/2016 11:36:25 - INFO - Flashing data

16/036/2016 11:36:26 - INFO - Processing rpm.sin

16/036/2016 11:36:26 - INFO - Checking header

16/036/2016 11:36:26 - INFO - Flashing data

16/036/2016 11:36:27 - INFO - Closing TA partition

16/036/2016 11:36:27 - INFO - Opening TA partition 2

16/036/2016 11:36:27 - INFO - Processing system.sin

16/036/2016 11:36:27 - INFO - Checking header

16/036/2016 11:36:27 - INFO - Flashing data

16/040/2016 11:40:45 - INFO - Processing userdata.sin

16/040/2016 11:40:45 - INFO - Checking header

16/040/2016 11:40:45 - INFO - Flashing data

16/041/2016 11:41:06 - INFO - Closing TA partition

16/041/2016 11:41:06 - INFO - Opening TA partition 2

16/041/2016 11:41:06 - INFO - Flashing cust-reset.ta to partition 2

16/041/2016 11:41:06 - INFO - Writing TA unit 000008A4. Value : 00 00 00 00 00 00 00 00 00 00 00 00 00 00

16/041/2016 11:41:06 - INFO - Closing TA partition

16/041/2016 11:41:06 - INFO - Opening TA partition 2

16/041/2016 11:41:06 - INFO - Processing elabel-C6503-row_201310181800.1_10.6.A.0.454.sin

16/041/2016 11:41:06 - INFO - Checking header

16/041/2016 11:41:06 - INFO - Flashing data

16/041/2016 11:41:08 - INFO - Closing TA partition

16/041/2016 11:41:08 - INFO - Opening TA partition 2

16/041/2016 11:41:08 - INFO - Writing TA unit 00002725. Value : 32 30 31 36 2D 30 37 2D 31 36 20 31 31 3A 34 31 3A 30 38 00

16/041/2016 11:41:08 - INFO - Writing TA unit 00002774. Value : 00

16/041/2016 11:41:08 - INFO - Closing TA partition

16/041/2016 11:41:09 - INFO - Ending flash session

16/041/2016 11:41:09 - INFO - Flashing finished.

16/041/2016 11:41:09 - INFO - Please unplug and start your phone