With the Auto Approve + Auto Login registration action, UsersWP creates the account, logs the user in and sends them to the page you chose. If new users end up logged out instead, work through these checks.

1. Check the form they used. Go to UsersWP > User Types, edit each user type and look at Registration Action. Every register form has its own setting, so one form can log users in while another does not.
2. Clear your page cache and exclude the UsersWP pages from caching. A cached page can make a logged in user look logged out. See Login Cache Issue, site showing logged out after login.
3. Look for a plugin conflict. Turn off your other plugins, register a test user, then turn the plugins back on one at a time and test after each. Security, SEO and login plugins are good ones to try first. The Health Check & Troubleshooting plugin lets you do this for your own session only, so visitors are not affected.
4. Switch to a default WordPress theme for a test, in case your theme changes login or redirects.

If the login itself fails, UsersWP shows the WordPress login error on the register form instead of redirecting. Note that message down if you contact support.

The page users land on after registering is set in the same place, in Redirect Page. That option only appears when Registration Action is Auto Approve + Auto Login.