This error appears to be the same as a resolved error for 8.0, see bug 246249

What happens:
If I have a file, lets say index.jsp, and two more files f0.jspf, f1.jspf. If I include f0.jspf and f1.jspf inside my index.jsp, any variables from f0.jspf are not visible from f1.jspf, but vars from f0.jspf are visible inside index.jsp according to netbeans 8.2, but it compiles and run just fine, tested on wildfly 10.

See code:
f0.jspf:
<%@ page pageEncoding="UTF-8" %>
<%
    String someString = "Hello";
%>

f1.jspf
<%@ page pageEncoding="UTF-8" %>
<%
    out.println(someString); //This is what netbeans says does not exists
%>

index.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@include file="WEB-INF/f0.jspf" %>
<%@include file="WEB-INF/f1.jspf" %>
<%
    out.println(someString);
%>

This has been very easy to reproduce, New Project -> Java Web -> Web Application
create files f0.jspf and f2.jspf inside WEB-INF, create file index.jsp (after removing index.html that was auto-created). Copy and past the code above for each file respectively. Run it and you should see 'Hello Hello' in your browser.  

I hope this is an easy fix!
Thank you,
Trevor Flynn