Groovy compare lists and remove in Jenkins error with contains

I'm running groovy in Jenkins. I have 2 lists that are created from a sh script. I need to format each item on list1 and then check if that value is in list2. If it is, I want to remove it from list2.

At first I was running into a lot of issues using .remove() so I've tried different implementations of .split() as List and tokenize() to avoid the No signature of method: java.util.ArrayList.remove() is applicable for argument types: (java.lang.String) values:

The problem is when I do my list2.contains(newName) it gives me false. I get true if I dont do the as List, but then I'm unable to use .remove() for reason above. I also tried to use the removeIf function, but get groovy.lang.MissingMethodException: No signature of method: java.util.ArrayList.removeIf() is applicable for argument types: (org.jenkinsci.plugins.workflow.cps.CpsClosure2) values: [org.jenkinsci.plugins.workflow.cps.CpsClosure2@3ab421bf]

Thanks for any help, this has been driving me crazy!

def list1 = []
def list2 = []

list1 = sh(script: """myscript""", returnStdout: true).split() as List
list2 = sh(script: """myscript""", returnStdout: true).tokenize()

list1.each { i -> 
    newName = "test-${i}"
    if (list2.contains(newName)) {
        list2.remove(newName) 
}
echo "${list2} // This doesn't change in Jenkins even when it should because the if statement isn't working.
          
            
 //Instead of if statement I've also tried:
 //chartList.removeIf { k -> k == chartName}

I've checked my classes as well:

println(list1.getClass())
> class java.util.ArrayList
println (list2.getClass())
> class java.util.ArrayList

Groovy Playground works with the removeIf and my if statement, which is how I know it must be something Jenkins.

def list1 = []
def list2 = []

list1 = ['orange', 'lime']
list2 = ['apple', 'orange', 'banana', 'pear']

list1.each { i ->

list2.removeIf { it -> it == i }

    //This also works:
       // if (chartList.contains(i)) {

       //     chartList.remove(i)
      
       // }
}
println list2