Actually, I didn't see anything weird in the log file today as you mentioned.
Here the log for today:
[2016/02/25 06:06:38 UTC] [EROR] /webdav/: code=404 ip=192.99.144.140
[2016/02/25 09:37:40 UTC] [EROR] /manager/html: code=404 ip=222.186.21.112
[2016/02/25 15:00:59 UTC] [EROR] /manager/html: code=404 ip=189.57.228.200
[2016/02/25 17:34:31 UTC] [EROR] /w00tw00t.at.blackhats.romanian.anti-sec:): code=404 ip=162.213.152.36
[2016/02/25 17:34:31 UTC] [EROR] /phpMyAdmin/scripts/setup.php: code=404 ip=162.213.152.36
[2016/02/25 17:34:31 UTC] [EROR] /phpmyadmin/scripts/setup.php: code=404 ip=162.213.152.36
[2016/02/25 17:34:31 UTC] [EROR] /pma/scripts/setup.php: code=404 ip=162.213.152.36
[2016/02/25 17:34:32 UTC] [EROR] /myadmin/scripts/setup.php: code=404 ip=162.213.152.36
[2016/02/25 17:34:32 UTC] [EROR] /MyAdmin/scripts/setup.php: code=404 ip=162.213.152.36
[2016/02/25 20:29:17 UTC] [EROR] /freepbx/admin/CHANGES: code=404 ip=104.192.0.18
[2016/02/25 20:45:49 UTC] [EROR] /freepbx/admin/CHANGES: code=404 ip=104.192.0.18
My guess is the proxy server (nginx) lost connection with the server. Please let me know if something I have to check from my side.
Thanks
Thileepan