It is putting an invalid command for every job configured to use the plugin:

20:00:38 [EnvInject] - Loading node environment variables.
20:00:38 Building on master in workspace /var/jenkins_home/workspace/mount-efs
20:00:38 [SSH] script:
20:00:38 =""
20:00:38 JENKINS_USER_PASSWORD=**********
20:00:38
20:00:38 echo ${JENKINS_USER_PASSWORD} | sudo -S – /usr/local/bin/mount_efs
20:00:38
20:00:38 [SSH] executing...
20:00:38 bash: =: command not found
20:00:38 [sudo] password for ****: EFS is already mounted. Exiting.
20:00:39
20:00:39 [SSH] completed
20:00:39 [SSH] exit-status: 0
20:00:39
20:00:40 Finished: SUCCESS