Tried Ubuntu, MX Linux and Debian in the last couple days and the CPU can only boot with Arch Linux (this comes with 5.5.6 kernel). So I guess this CPU have some compatbility issues with Unraid or other Linux with earlier Kernels. Maybe I should try Unraid 6.9.0-BETA1 coz it's kernel has been updated to 5.5.8.
To eliminate the chance of a faulty processor, I also ran Prime 95 for 24 hours on Windows 10 without any issues, so I think the CPU should be in good shape.