Today something weird happened with my computer. First it hang and I couldn't move the mouse anymore, then I hard rebooted it and it couldn't find my root partition anymore. I thought the SSD broke so I switched it to a different computer and it works fine there. I put in a new SSD and the new one has the same problem.
Then the bios tells me that the date is not set, while setting the date I see that the SATA setting is set to Raid, while I remember that I set it to AHCI when I installed my OS for the first time.
Setting it back to AHCI resolved the issue and I can boot again. It seems somehow the bios settings reset them selves to default or something.