I fixed this, problem with Nginx conf for that site.
I had something like this in my conf:
if ($request_uri ~* "^(.*/)index\.php/?(.*)") {
return 301 "$1$2";
}
I just commented it out, restarted Nginx and it worked.
I’m not an expert with Nginx but I think that it’s matching anything before and after index.php rewriting the url and then redirecting you via 301 permanently moved. In my testing I found it didn’t match all the parameters after .php? and that broke Piwik.
But again, not an expert. Just my limited understanding.