That log is really helpful 
The installer is able to download the image archive, unlock the bootloader, unpack the archive, but then fails as soon as it tries to flash the first partition.
That happens in line 127 of flash-scripts/windows/emerald-install-from-bootloader.bat · master · e / devices / Easy Installer · GitLab
The command there is
%FASTBOOT_PATH% -s %DEVICE_ID% flash %%partition_name[%%i]%% %%partition_image[%%i]%%
which gives the error
fastboot: error: cannot load '%partition_image[0]%': No such file or directory
I’m not an expert on windows CMD scripting, but my interpretation is that the variable name “partition_image[0]” gets passed to fastboot instead of the variable’s value "gz.img " defined at the top of the script.
Note: I’m looking at the latest version of the script which might not be the one used in the released installer package.
Don’t have much time right now, but at least I wanted to share the result of my log analysis.
Edit: although I can’t test it myself, it should work if the script was changed to
(for /L %%i in (0,1,10) do (
setlocal enableDelayedExpansion
%FASTBOOT_PATH% -s %DEVICE_ID% flash !partition_name[%%i]! !partition_image[%%i]!
if errorLevel 1 ( exit /b !partition_error[%%i]! )
timeout 1 >nul 2>&1
call echo "Flashed %%partition_name[%%i]%% "
))
For some reason, variable substitution seems to be different for “echo” and other commands 