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Discovered that "flux" was running the dhcpd service. Sheesh... I thought I had turned it off, but it must have been re-enabled as part of the system rebuild.
dhcpd on flux was giving address 192.168.0.163 to 00:20:f6:05:1e:d5, which is pingable, but which explains why it didn't respond to 192.168.0.137.
It was also giving out these addresses:
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