There are certain times that the registration is handled by other plugins, however WP User Manager automatically generates a password during registration.
To deactivate this feature, you may download and save this file to your /wp-content/mu-plugins/ directory (you might need to create the mu-plugins directory). – wpum_do_not_generate_password.php
add_filter( ‘wpum_new_user_notification_generate_password’, ‘__return_false’ );
Get Started with the Best WordPress Membership Plugin Today
Connect, Manage and Build your Membership Site