Random reboots how to diagnose? Also lower Geekbench than expected?

Hi, my system has random reboots and I'm not sure how to diagnose the issue. Can you point me in the right direction?

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Specs:

• i7-8700K
• 32gb Ram
• SMBIOS MacPro6,1
• RX 580
• M.2 512 GB EVO SSD

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Also, my Geekbench is lower than the standard on Geekbench for an i7-8700K

Mine: https://browser.geekbench.com/v4/cpu/12433847

Standard: https://browser.geekbench.com/processors/2062