Throttle Concurrent Builds & open PR

Hello everyone,
I am using the “Throttle Concurrent Builds” plugin but I am having problems.

I set up on Jenkins (Manage Jenkins → System) the Multi-Project Throttle Categories as follow:
Category name: pipeline_ms_throttle
Maximum Total Concurrent Builds: 2
Maximum Concurrent Builds Per Node: 2

In my jenkins file I set up:

pipeline {
  agent {
    node {label 'LINUX'}
    // Throttle a declarative pipeline via options
  options {
      categories: ['pipeline_ms_throttle'],
      throttleEnabled: true,
      throttleOption: 'category'

Now, if I try to run multiple pipelines at the same time the plugin seems to work correctly


However, if I go to do a merge in a branch (Ex: dev) that has several Pull Requests open, the builds of these PRs restart at the same time without considering the plugin.

How is this possible in your opinion? Is there a solution to this problem?

Thanks in advance