I have created a property files with vars either initialized to a constant value or to another var coming from the Jenkins instance global properties.
Then, I create a Jenkinsfile starting with a node block which reads the property file :

def myEnv
node {
 myEnv=
readProperties( file:fileName, interpolate:true )

}
pipeline {
 ...
}

Most of vars are correctly set as far as I can check that their value. But few of them are not interpolated. Those I am concerned with are initialized with a global jenkins variable which is either initialized itself as a constant value or using another global variable.
But some others initialized the same are correctly interpolated.
So... I am a bit lost.
Additionally, I tried with interpolate:false ... and surpringly the results was not worst ! It means that variables are interpolated... unless the few that are not.