After a Drupal based site came out of the maintenance mode, one particular web page was found to be stuck in the maintenance mode. It showed the message that the site was under maintenance, while the other web pages were displayed correctly.
The problem was resolved by clearing the cache. In the administrative menu, the
Flush all caches option was clicked. In retrospect, it appears that it is a good practice to clear the cache after bringing a site online from the maintenance mode.