I have a job with no label restriction and master without executors. The job seems to be never scheduled:
Looking nodes where the poll can be run.
Looking for a candidate node to run the poll.
Looking for a node with no predefined label.
Trying to poll with the last built on node.
Trying to poll on master node.
Finding Jenkins but it is not eligible.
Can't find any complete active node for the polling action.
Maybe slaves are not yet active at this time or the number of executor of the master is 0.
Checking again in next polling schedule.
The problem seems to be that org.jenkinsci.lib.xtrigger.AbstractTrigger treats jobs without label expression as if it slave without labels. It should run anywhere instead.