When matrix jobs are using node labels, the builds are always pending even if nodes are available with the specified labels.

When using nodes names, the builds are ok.

In the first case, if we execute the script https://support.cloudbees.com/hc/en-us/articles/235690727-Why-are-jobs-on-the-queue-when-there-are-dedicated-slaves-with-free-executors , the logs are filled with the following cause :

JobOffer[Nodes-xxxx-1 #0] refused hudson.model.Queue$BuildableItem:hudson.matrix.MatrixProject@1c83d0a1[XXXX_xx]:46
because of Don't run FlyweightTask on vSphere node.