We had the same problem, with one of our 5 lockable resources. We downgraded to 1.11.2 and updated all configuration using the plugin and everything is working like before.

Also same problem with 2.0, generated jobs.

At first, one job holds the resource, the other one waits, resource is showing as queued.

After a short delay, the second job suddenly starts, the resource itself switches to "unlocked" state, and the second job shows the empty brackets: [].

Now both jobs are running simulataniously and the resource is incorrectly unlocked.

For cross reference: https://github.com/jenkinsci/lockable-resources-plugin/issues/54

debfx pointed out that version 2.0 creates invalid configurations:

    <org.jenkins.plugins.lockableresources.RequiredResourcesProperty plugin="lockable-resources@1.11.2">
      <resourceNames>ResX ResY</resourceNames>
      <resourceNamesVar></resourceNamesVar>
      <resourceNumber></resourceNumber>
      <labelName></labelName>
    </org.jenkins.plugins.lockableresources.RequiredResourcesProperty

while the previous version serialized into a configuration like this:

    <org.jenkins.plugins.lockableresources.RequiredResourcesProperty plugin="lockable-resources@1.11.2">
      <resourceNames>ResX ResY</resourceNames>
    </org.jenkins.plugins.lockableresources.RequiredResourcesProperty>

Note how the missing (nulled) options were replaced by empty options instead?

Unbreaking the configuration also works again with 2.0. Using the broken 2.0 configuration with 1.11.2 also triggers the bug.

I believe I found a solution for this in the plugin code. In RequiredResourcesProperty.java there is this snippet in the RequiredResourcesProperty constructor. 

this.resourceNames = resourceNames;
this.resourceNamesVar = resourceNamesVar;
this.resourceNumber = resourceNumber;

The label name is set a little further down in the same way. It looks like these are getting set to an empty string when they should be getting set to null. I just added a little type checking and it works for me. 

this.resourceNames = resourceNames;
if (resourceNamesVar.equals("")) {
this.resourceNamesVar = null
} else {
this.resourceNamesVar = resourceNamesVar;
}
if (resourceNumber.equals("")) {
this.resourceNumber = null
} else {
this.resourceNumber = resourceNumber;
}

This fixes the job config issue pointed out by Andreas. 

@abayer: Are you aware of this? We still have this issue in version 2.1

Set up a PR to get that one done.

Code changed in jenkins
User: krull
Path:
src/main/java/org/jenkins/plugins/lockableresources/RequiredResourcesProperty.java
src/test/java/org/jenkins/plugins/lockableresources/BasicIntegrationTest.java
http://jenkins-ci.org/commit/lockable-resources-plugin/1e440bfbbd803400065c062ae6bba9b86a7e45ac
Log:
JENKINS-43574: fix construction of RequiredResourcesProperty

Code changed in jenkins
User: krull
Path:
src/main/java/org/jenkins/plugins/lockableresources/RequiredResourcesProperty.java
http://jenkins-ci.org/commit/lockable-resources-plugin/90bee03e8972183210ca5510f4e276bc8097cdb7
Log:
JENKINS-43574: replace whitespaces with tabs

Code changed in jenkins
User: Antonio Muniz
Path:
src/main/java/org/jenkins/plugins/lockableresources/RequiredResourcesProperty.java
src/test/java/org/jenkins/plugins/lockableresources/BasicIntegrationTest.java
http://jenkins-ci.org/commit/lockable-resources-plugin/67a01b44f4a995955e0888db62f927fcc740697a
Log:
Merge pull request #89 from krulls/master

JENKINS-43574: fix construction of RequiredResourcesProperty

Compare: https://github.com/jenkinsci/lockable-resources-plugin/compare/3b9717e389f7...67a01b44f4a9

Released as 2.2