Due to a change introduced this morning to our BusyBox source, to flash a new nightly moving forward you must do a one-time manual process.
Download tonight’s (2/14) nightly, unpack the zip and use fastboot to flash the boot.img.
Command:
fastboot flash boot boot.img
This will allow you to resume the normal update process. Sorry in advance for the hassle, but this was a necessary change for how mounts are handled in BusyBox. As Sony devices use a combined boot and recovery.img (no separate recovery partition), fastboot is the only way to workaround this latest change.