Reproduction steps

1. Set the following config for priority-sorter

priorityConfiguration:
  jobGroups:
    - jobGroupStrategy: "allJobs"
      priority: -1
      priorityStrategies:
        - buildParameterStrategy:
            parameterName: "PRIORITY"
        - userIdCauseStrategy:
            priority: 4
      usePriorityStrategies: true
prioritySorterConfiguration:
  onlyAdminsMayEditPriorityConfiguration: true
  strategy:
    absoluteStrategy:
      defaultPriority: 5
      numberOfPriorities: 7

2. Start Jenkins with the above configuration

Observed result

The actual value of the userIdCausePriority is 3 as can be shown by extracting the configuration of the plugin from the instance of Jenkins.

priorityStrategy:
  userIdCauseStrategy:
    priority: 3

Expected result

The expected value of the userIdCausePriority is 4 as defined in the input configuration file.

priorityStrategy:
  userIdCauseStrategy:
    priority: 4

Root cause

The 'scale' method in PriorityCalculationsUtil seems to be called when the JCasC configuration is being applied. The method returns distorted results due to numerical anomalies - apparently the actual float values are a little smaller/bigger than expected ones (e.g. 0.3(9) instead of 0.4) so the used 'floor' and 'ceil' functions may lead to wrong results.