After the recent BIOS update I'm not able to start Ubuntu. I found the solution to this problem here: Gave up waiting for root device on Ubuntu
Apparently after the update the SATA operation changed from AHCI to RAID on. I tried to switch back to AHCI, but every time I exit the BIOS it resets this option to RAID on.
I thought that maybe motherboard battery is too old, but other option are saved correctly after change.
My laptop is Dell xps 15 9500.