SanDisk Ultra+ SSD Manual Firmware update version X2316RL

Had same problem and thought it was a problem with my Asus Rampage motherboard but it wasn’t.
Just removed the serial line as everyone already mentioned and updated right away after failing every other way I tried i.e. via Windows Sandisk firmware update and using bootable ISO image.
Can’t believe they never bothered to fix this since how long has this firmware been out?