I can see from the log that the plugin correctly replaces the / fields in the job name with - characters.
Using remote perforce client: SDMOS-dev-mjou-__sdmos_sdmos-int-ucom-build-Build_SDMOS_ucom_CDC_arm.local_jenkins_mlb-2062542078
But the P4CLIENT is still set to using a client with /
User name: jenkins
Client name: SDMOS/dev/mjou/__sdmos_sdmos-int/ucom/build/Build_SDMOS_ucom_CDC_arm.local_jenkins_mlb-2062542078 (illegal)
Any call i then do that needs P4CLIENT fails with an error about slashes not allowed in P4CLIENT