Maybe you've already done this, but if not:
Put this tag on the Login page and any post-login landing page:
<p>CONTEXT: [[!GetContext]]</p>
Then create a snippet called GetContext with this code:
return $modx->context->get('key');
BTW, make sure you're previewing from the Manager, and make sure you're not logged in to the Manager when you test. That confuses you're front-end login status.
I usually test in another browser (a separate window is not enough), where I'm not logged in to the Manager.