There are instances where the node titles disappear for updated nodes. The site uses organic groups with APC for caching data. The drupal version installed is 7.18 however most modules including entity, token, entity token etc are up to date. The site has few custom modules and rules enabled but they do not affect the node title. I suspect there may be issue with cache which results in instances when node titles are not populated. Please do suggest ways in which I would be able to figure out the exact issue.