Could it be that you also upgraded php at the time you updated to Elgg 1.12? Possibly, the php variable session.gc_maxlifetime in php.ini isnt't set to the default value since then and that might be the reason the session times out after 5 minutes already. I would suggest to check the value of session.gc_maxlifetime and possibly the other session.gc.* php variables in php.ini and set them to the default values if the values are different.

Also, when I do elgg_language_key_exists('cp_notify:footer2','fr'); the return value is false but my key does exists.

resolved,