With version 2.3 of Lockable resources plugin we experience the same error described in JENKINS-43574:
09:59:21 Started by timer
http://jenkinsaris:8080/view/__ALL_dev_U__trunk_/job/MS___ALL_dev_u__trunk__Team_SAP/44/console#L609:59:21 [lockable-resources] acquired lock on []
http://jenkinsaris:8080/view/__ALL_dev_U__trunk_/job/MS___ALL_dev_u__trunk__Team_SAP/44/console#L709:59:21 [EnvInject] - Loading node environment variables.
It was fixed in 2.2. Did it return with 2.3 version?
As temporary solution we will switch back to version 2.2.
We are seeing this issue in 2.7. It happens randomly.