This issue occurs because MACsec is only supported on specific MICs/PICs. Not all ports on the MX10003 support MACsec functionality.

Diagnosis:

Use the command "show chassis hardware detail no-forwarding" to check the installed hardware.
Verify which PICs support MACsec. For example:

PIC 0 (6xQSFPP): Does NOT support MACsec
PIC 1 (MIC1-MACSEC): Supports MACsec


Hardware Support:

Without MACsec support: JNP-MIC1
With MACsec support: JNP-MIC1-MACSEC

Additional Information:

Starting with Junos OS Release 18.3R1, you can use the Mellanox 10-Gbps pluggable adapter (QSFP+ to SFP+ adapter or QSA; model number: MAM1Q00A-QSA) to convert four lane-based ports to a single lane-based SFP+ port.
The QSA adapter can be used to convert a 40-Gbps port to a 10-Gbps or a 1-Gbps port.
The 4x10 Gbps ports on the 6xQSFPP PIC and the QSFP28 ports on the non-MACsec MIC (JNP-MIC1) can be configured in 1-Gbps mode when an SFP is plugged in through the QSA adapter.

Recommendation:
Ensure that MACsec is only configured on supported MICs/PICs, such as the JNP-MIC1-MACSEC.


For more information about MIC compatibility, refer to the MX10003 documentation:
https://www.juniper.net/documentation/us/en/hardware/mx10003/mx10003.pdf


Note: Always verify the compatibility of MICs and PICs with your specific Junos OS version and hardware configuration.