Darn. Does this mean I should run memtest? I have ECC RAM, and I've come across a post (by @johnnie.black!) that says memtest doesn't really help. I have a Supermicro X10SDV-TLN4F, which has IPMI.

Some motherboard have a function in BIOS that allows to deactivate ECC.

If it is your case, then you can perform Memtest.

13 minutes ago, sonofdbn said:

I have ECC RAM,

If that's the case then it shouldn't be a RAM problem, could still be a hardware problem, like controller or actual device.

Thanks for the quick replies. OK, I might just change the SSD - or is there a chance it's a SATA cable problem?

9 minutes ago, sonofdbn said:

or is there a chance it's a SATA cable problem?

Unlikely.