I have upgraded to OJS 2.4.3
Since then, only the whole OJS directory is not accessible between 9-10 am (gmt+2 time zone).
Here is the journal: http://www.j-humansciences.com/ojs/index.php
There is no any back up program running, no cron job.
I don't know what causes, every morning exactly at 9:00 am, OJS shots down, completely blank page, noting seen.
One hour later, at 10:00 am, it is live again.