Index: tests/phpunit/testcases/core/nav/bpCoreNewSubnavItem.php
===================================================================
--- tests/phpunit/testcases/core/nav/bpCoreNewSubnavItem.php
+++ tests/phpunit/testcases/core/nav/bpCoreNewSubnavItem.php
@@ -335,4 +335,45 @@
 
 		$this->assertSame( 'bar', buddypress()->bp_options_nav['parent']['foo']['css_id'] );
 	}
+
+	/**
+	 * @ticket BP7931
+	 */
+	public function test_subnav_should_not_404_on_early_bp_setup_nav_priority() {
+		$u = self::factory()->user->create();
+		$old_current_user = get_current_user_id();
+		$this->set_current_user( $u );
+
+		$user_domain = bp_core_get_user_domain( $u );
+
+		// Register a subnav on 'bp_setup_nav' hook early (at priority zero).
+		add_action( 'bp_setup_nav', function() use ( $user_domain ) {
+			/*
+			 * Emulate a subnav screen.
+			 *
+			 * The bp_core_load_template() call is imperative for our 404 check to work!
+			 */
+			$screen = function() {
+				bp_core_load_template ('members/single/plugins');
+			};
+
+			// Register the subnav.
+			bp_core_new_subnav_item( array (
+				'name'            => 'Testing',
+				'slug'            => 'testing',
+				'parent_url'      => $user_domain . bp_get_profile_slug (). '/',
+				'parent_slug'     => bp_get_profile_slug (),
+				'screen_function' => $screen,
+				'position'        => 20
+			) );
+		}, 0 );
+
+		// Emulate visit to our new subnav page.
+		$this->go_to( $user_domain . bp_get_profile_slug () . '/testing/' );
+
+		// Assert that subnav page does not 404.
+		$this->assertFalse( is_404() );
+
+		$this->set_current_user( $old_current_user );
+	}
 }