We are tracking traffic with Piwik on our pltaform using the JS Tracker API.
Our platform is managing multiple web sites, each gets a different site id.
We saw that for every web site there is a triplet of cookie created by piwik - _pk_id, _pk_ref, _pk_sess
After getting several of these - the web server suddenly returns a 400 bad request and cannot load the relevant site. When deleting the cookies it all returns to normal.
We are not sure if this is the number of cookies that is causing it or rather the contents of the cookie.
This is really urgent as I cannot instruct users to delete cookies…all over the web.