Hi Kim and Everyone,
I am also experiencing a similar issue. Check out my thread, Forum NG:CANNOT SEE FORUM POSTS (https://moodle.org/mod/forum/discuss.php?d=254706).
Although someone decided to change the Subject Line of my post to reflect ForumNG, I am actually referencing Moodle's inherent/embedded Forum module.
As an update to your thread, I have printed out all of the permissions for my entire site/forum and checked off any possible misconfigurations as was suggested (one by one, to no avail) that would inhibit all users from seeing any forum responses. Hopefully someone can steer us in the right direction....