JMeter While Controller failing - while-loop

Question

I want to be able to run multiple iterations of this test plan.
Thread Group
While ${__javaScript("${user}" != "<EOF>",)}
csv1 config
If "${user}" != "<EOF>"
Module Controller
While ${__javaScript("${user2}" != "<EOF>",)}
csv2 config
If "${user2}" != "<EOF>"
Module Controller 2
When I run the test, at the end of the 2nd while controller, it outputs the following error:
I've also tried running just 1 of the while controllers, and it has the same response. I'm not sure why it doesn't stop the current iteration and start a new one if it's able to get to the 2nd while controller.
java.lang.StackOverflowError: null
at java.lang.Class.getDeclaredFields0(Native Method) ~[?:1.8.0_231]
at java.lang.Class.privateGetDeclaredFields(Unknown Source) ~[?:1.8.0_231]
at java.lang.Class.getDeclaredField(Unknown Source) ~[?:1.8.0_231]
at jdk.nashorn.internal.runtime.Context$ContextCodeInstaller$1.run(Context.java:209) ~[nashorn.jar:?]
at jdk.nashorn.internal.runtime.Context$ContextCodeInstaller$1.run(Context.java:204) ~[nashorn.jar:?]
at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_231]
at jdk.nashorn.internal.runtime.Context$ContextCodeInstaller.initialize(Context.java:204) ~[nashorn.jar:?]
at jdk.nashorn.internal.codegen.CompilationPhase$InstallPhase.transform(CompilationPhase.java:508) ~[nashorn.jar:?]
at jdk.nashorn.internal.codegen.CompilationPhase.apply(CompilationPhase.java:624) ~[nashorn.jar:?]
at jdk.nashorn.internal.codegen.Compiler.compile(Compiler.java:655) ~[nashorn.jar:?]
at jdk.nashorn.internal.runtime.Context.compile(Context.java:1317) ~[nashorn.jar:?]
at jdk.nashorn.internal.runtime.Context.compileScript(Context.java:1251) ~[nashorn.jar:?]
at jdk.nashorn.internal.runtime.Context.compileScript(Context.java:627) ~[nashorn.jar:?]
at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:535) ~[nashorn.jar:?]
at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:524) ~[nashorn.jar:?]
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:402) ~[nashorn.jar:?]
at jdk.nashorn.api.scripting.NashornScriptEngine.eval(NashornScriptEngine.java:155) ~[nashorn.jar:?]
at org.apache.jmeter.functions.JavaScript.executeWithNashorn(JavaScript.java:142) ~[ApacheJMeter_functions.jar:5.1.1 r1855137]
at org.apache.jmeter.functions.JavaScript.execute(JavaScript.java:103) ~[ApacheJMeter_functions.jar:5.1.1 r1855137]
at org.apache.jmeter.engine.util.CompoundVariable.execute(CompoundVariable.java:136) ~[ApacheJMeter_core.jar:5.1.1 r1855137]
at org.apache.jmeter.engine.util.CompoundVariable.execute(CompoundVariable.java:111) ~[ApacheJMeter_core.jar:5.1.1 r1855137]
at org.apache.jmeter.testelement.property.FunctionProperty.getStringValue(FunctionProperty.java:101)
...
Thanks in advance.

Answer 1

It might be connected with the test data, check the last line(s) of your 2nd CSV file, there might be a blank line or non-printable character which is causing errors.
Since JMeter 3.1 it's recommended to use JSR223 Test Elements and Groovy language for scripting so consider migrating to __groovy() function in the While and If Controllers. The equivalent Groovy expression would be:
${__groovy(!vars.get("user2").equals("<EOF>"),)}
where vars is the shorthand for JMeterVariables class instance, check out Top 8 JMeter Java Classes You Should Be Using with Groovy article for more information on this and other JMeter API shortcuts
It's also recommended to always use the latest version of JMeter so consider migrating to JMeter 5.2.1 (or whatever is the most recent stable JMeter version which is available at JMeter Downloads page)

Answer 2

I didn't know how Loop Controllers worked, but I used them to solve this problem.
Thread Group
Throughput Controller
Loop Controller (size_of_csv)
csv config
Module Controller
Loop Controller 2(size_of_csv 2)
csv 2 config
Module Controller 2