Not tracking visits after upgrade to 2.16.5

After upgrading from 2.16.2 to 2.16.5 my piwik instance has stoped logging visits. The visits show up in the Visitor Log (in the piwik web UI) but the Vists graph shows zero visits and if I select a single day (after the upgrade), it has zero visits.

Piwik 2.16.5 wp 4.6.1, nginx+php5-fpm+mariadb on Debian Jessie (stable)

nginx, php, mariadb are up and running, I can access the web UI, the tracked web sites contacting piwik (I see it in the webserver access log).

I did a manual upgrade from CLI disabling piwik web UI and piwik tracking

record_statistics = 0
maintenance_mode = 1

Where could I start digging to find the root of this issue?

Probably found the reason:

I had to change the document root location for piwik in nginx, but left the old path in the /etc/cron.d/piwik-archive cron job.