Website is ... http://www.breakfreeclub.com

Steps to reproduce the issue

Attempt to Login with an existing user
Sign-up as a new user, then login.

Expected result

Redirect to a specific Welcome Page post Login

Actual result

Returns to Home Page
Started with Joomla 3.6.5 to 3.7.0 upgrade ... and subsequently upgraded to 3.7.2 (no change in result)

Logout does redirect properly to Login page as requested in Logout Menu Item ... but for some obscure reason, Login won't redirect. This is also the same for the Login Module (login redirect fails, logout redirect works)

System information (as much as possible) - Pretty native install really.

PHP Built On Linux sg2plcpnl0094.prod.sin2.secureserver.net 2.6.32-673.26.1.lve1.4.25.el6.x86_64 #1 SMP Wed Apr 5 16:33:01 EDT 2017 x86_64
Database Version 5.6.35-cll-lve
Database Collation latin1_swedish_ci
Database Connection Collation utf8mb4_general_ci
PHP Version 5.6.30
Web Server Apache/2.4.25
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 3.7.2 Stable [ Amani ] 22-May-2017 09:46 GMT
Joomla! Platform Version Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36

Additional comments - Have 4 extensions installed - none doing anything that should affect this simple redirect.

1. Full Screen 10 Template
2. Kunena Forum (uses default Joomla User Management)
3. Membership Pro Subscription Engine (uses default Joomla User Management)
4. Supersize Images

Extra Info / Actions Tried To Fix

I've tried creating a new Login menu item (to User > Login Form) ... same result
I've created a Login Module and tried that as well ... same result
I've cleared cache and trash

When I edit the Menu Item, I set the Login Options to redirect to a Menu Item (not a URL)

Menu Item > Login Form (using default Login Form not Login Module and has Guest ACL), it redirects back to home page instead of following redirect to new Menu Item.

I'm lost and the only thing I have left is that it's some kind of joomla bug. It's supposed to redirect to the Welcome Members page which has a menu item (I've tried top level and sub-menu ... same result on both).

Help appreciated ... driving me crazy.

Also, is there a tool I can use to step through the code as it's executing line by line to see what variables are being passed by the Login button and to see if anything is being set?