On a QFX5120-48T, when a link is enabled, the below log messages may be seen:
Dec 7 16:30:02 lab-QFX5120-48T fpc0 PORTDEV: DEVSTART TX enable/disable failed for port: xe-0/0/26
Dec 7 16:30:02 lab-QFX5120-48T fpc0 PORTDEV: DCBCM optic Tx enable for xe-0/0/26
Dec 7 16:30:02 lab-QFX5120-48T fpc0 PORTDEV: Forcing delayed devstart for xe-0/0/26

The below log messages may be seen when ports are enabled:
Dec 7 16:30:02 lab-QFX5120-48T fpc0 PORTDEV: DEVSTART TX enable/disable failed for port: xe-0/0/26
Dec 7 16:30:02 lab-QFX5120-48T fpc0 PORTDEV: DCBCM optic Tx enable for xe-0/0/26
Dec 7 16:30:02 lab-QFX5120-48T fpc0 PORTDEV: Forcing delayed devstart for xe-0/0/26

These log messages are seen because the Optic Enable Function is being called even though the port is an RJ45 Port. These messages are not harmful and can be safely ignored and/or filtered. The problem has been addressed in the following releases via PR 1754789: 21.4R3-S6 22.1R3-S5 22.2R3-S3 22.4R3 23.2R2 23.4R1 23.4R2 24.1R1. Please check the PR for a compilation of releases that have resolved this issue.