I submit the following little program as an example of how you can
study such problems yourself in a kind of experimental way. However,
it doesn't find "AB(CDE", nor do I see how it could when the branch
that matches the opening "(" ends with the closing ")".

To match the closing paren before a word boundary there has to be a
word character immediately after it.

import java.util.regex.Pattern;
import java.util.regex.Matcher;
class Foo {
   public static void main(String [] _) {
    String pattern = "\\b[A-Z]("
       +   "[A-Z0-9]"
       +   "|[-+_/&.](?=[A-Z0-9])"
       +   "|[(][A-Z0-9]([A-Z0-9]|[-+_/&.](?=[A-Z0-9]))*[)]"
       +   ")+\\b";

    String text = "First AB(CDE) ends at a non-word-boundary, "
       + "second GH(IJ)K ends at a word-boundary."
       + "Third LM(NOP)q should be caught.";

    Matcher m = Pattern.compile(pattern).matcher(text);
    while (m.find()) {
       System.out.println(m.group());
    }
   }
}