Link from QFX5120-48T using  QSFP-100G-SR4-T2 flaps frequently.

Link flaps frequently and FEC errors are incrementing.

user@switch> show version | match Junos:
Junos: 22.2R3.15

user@switch> show interfaces et-0/0/X | match flapped
Last flapped : 2024-04-05 09:22:57 UTC (00:00:01 ago)

user@switch> show interfaces et-0/0/X | match FEC
Ethernet FEC Mode : FEC91
Ethernet FEC statistics Errors
FEC Corrected Errors 480
FEC Uncorrected Errors 70699
FEC Corrected Errors Rate 0
FEC Uncorrected Errors Rate 0

Issue was resolved after disabling the FEC91 on both sides

set interfaces et-0/0/X ether-options fec none

user@switch> show interfaces et-0/0/X | match FEC
Ethernet FEC Mode :          NONE
Ethernet FEC statistics       Errors
FEC Corrected Errors          0
FEC Uncorrected Errors         0
FEC Corrected Errors Rate        0
FEC Uncorrected Errors Rate       0

NOTE: Disabling or enabling FEC configurations may cause the interface goes down for some seconds.  You may want to apply the configuration in a maintenance window.

2024/11/21 -Publishing this KB

2026-05-07 : Modified the solution removing customer data.

2026-06-15 : Added a note about the impact of configuring FEC settings.