The other thing that gets mentioned in a lot of these threads, swap out the CMOS battery with a fresh one.
Beyond that, have you tried disabling CPU cores and hyperthreading? I know it's not really a solution though, but it could be related to the microcode updates for Spectre/Meltdown/etc.
If that does work, you could try using UBU to update the microcode in the BIOS to the latest. Obviously done at your own risk, but probably not much to lose at this point. Plus you have BIOS flashback.
Beyond that, have you tried disabling CPU cores and hyperthreading? I know it's not really a solution though, but it could be related to the microcode updates for Spectre/Meltdown/etc.
If that does work, you could try using UBU to update the microcode in the BIOS to the latest. Obviously done at your own risk, but probably not much to lose at this point. Plus you have BIOS flashback.