Cannot apply modification in Multijob configuration

[antoine-mg]

Hello Team,
It is not possible to modify any item of a (new or existing) MultiJob project from the Jenkins interface.
Multijob plugin is 1.36

E.g. : I want to change Phase name to "SWINT"
An error pop-up with no message when I try to apply changes :

I'm required to do it "manually" from the config.xml file and restart Jenkins server to get the configuration modified :

I verify that computer user has full control of the JENKINS_HOME folder/subfolder, and subfolders files are not read-only.
Does someone know how to solve it ?