Best regards. What's going on internally when I get this warning.
Warning: Unknown block versions are being mined! Unknown rules may be active
Bitcoin Core version v0.17.1 (64-bit)
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This warning is currently benign and has been fixed for Bitcoin Core 0.18. You see it because miners are using the block version number for a mining optimization called ASICBOOST. However soft forks in the past have used the version number for readiness signalling. Bitcoin Core is seeing version numbers it is not expecting (due to ASICBOOST) and thus triggering the warning.