On-box logging does not work with stream mode on SRX5K devices.

No traffic logs will be seen in the messages log file. 

SRX 5000 series do not send session logs to the Routing Engine (RE) in stream mode. Since system logging is done on the RE, that means that session or traffic logs cannot be written to the RE file system. Therefore all traffic logging must be sent to external syslog server. Furthermore since fxp0 belongs to the RE, the syslog server must be reachable by an interface on an IOC. Traffic logging cannot be sent out fxp0.

When the logging mode is set to stream, security traffic logs generated in the data plane are streamed out a revenue traffic port directly to a remote server. That also means your local log file will stop logging.

Check the logs on the syslog server to confirm if the corresponding logs are being received or not.

Note: On-box logging works with stream mode on the following devices,

vSRX 2.0, SRX 1500, SRX 4100, SRX 4200, SRX4600 and vSRX3.0

Please find the below kb.

https://supportportal.juniper.net/s/article/SRX-How-to-save-traffic-log-under-Stream-mode

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