Assume One Hardware Clock per NIC - UG1602

Assume multiple PTP Hardware Clock (PHC) devices presented by the same PCI® device represent the same underlying clock, which is often the case for third party NICs. This is enabled by default until version 3.7.1, and disabled by default from version 3.8.0 onwards. To disable:

[general]
assume_one_phc_per_nic off

See the assume_one_phc_per_nic option in Configuration Options.