To make sure that the software works, the latest and most suitable drivers should be installed directly from Sony. Often it can happen that Windows automatically installs the wrong drivers. To fix the problem, please manually select the correct drivers for the device.
The Sony drivers can be downloaded directly from the developer area: https://developer.sony.com/develop/drivers/
If the wrong drivers have been installed, XperiFIX will not be able to control the device properly via ADB / Fastboot.
Here are example screenshots from the Windows Device Manager with a connected Sony Xperia XZ Premium device (G8141):
Device in fastboot/bootloader mode:
Device in TWRP:
Tip: Sometimes you have to force installation of the Sony drivers. Some users reported that they have to disable the Windows driver verification on their computers. If your device is listed as a complete other device and you are sure the connected mode is correct, please uninstall the device from the Windows device manager (with enabled “delete related driver” checkbox) and install the driver manually (select from drivers list).