WP-Piwik stopped tracking visitors

Starting two days ago, my Piwik stopped tracking my visitors: I got 0 visitors for three days straight now. I had visits tough, I have accessed my site from another PC several times to test this.

This is my site (it’s german): http://flugplatz.tagblatt.de/

The Piwik version is 2.0.3 and the WP-Piwik version is 0.9.9.18.

If it helps, here’s my test script:

*** Test 1/2: SitesManager.getSitesWithAtLeastViewAccess ***
Using: cURL
SSL peer verification: enabled
User Agent:
Call: http://flugplatz.tagblatt.de/Piwik/piwik/?module=API&method=SitesManager.getSitesWithAtLeastViewAccess&format=XML&token_auth= + TOKEN
Result:
HTTP/1.1 200 OK
Date: Fri, 17 Apr 2015 10:09:17 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: PIWIK_SESSID=7fcaa08279509a46d7087fc281b8321d; path=/; HttpOnly
Transfer-Encoding: chunked
Content-Type: text/xml; charset=utf-8

<?xml version="1.0" encoding="utf-8" ?>
<result>
	<row>
		<idsite>1</idsite>
		<name>flugplatz.tagblatt.de</name>
		<main_url>http://flugplatz.tagblatt.de</main_url>
		<ts_created>2014-02-28 10:32:54</ts_created>
		<ecommerce>0</ecommerce>
		<sitesearch>1</sitesearch>
		<sitesearch_keyword_parameters />
		<sitesearch_category_parameters />
		<timezone>Europe/Berlin</timezone>
		<currency>USD</currency>
		<excluded_ips />
		<excluded_parameters />
		<excluded_user_agents />
		<group />
		<type>website</type>
		<keep_url_fragment>0</keep_url_fragment>
	</row>
</result>
Time: 0.07s

*** Test 2/2: SitesManager.getSitesIdFromSiteUrl ***
Using: cURL
SSL peer verification: enabled
User Agent:
Call: http://flugplatz.tagblatt.de/Piwik/piwik/?module=API&method=SitesManager.getSitesIdFromSiteUrl&url=http%3A%2F%2Fflugplatz.tagblatt.de&format=XML&token_auth= + TOKEN
Result:
HTTP/1.1 200 OK
Date: Fri, 17 Apr 2015 10:09:17 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: PIWIK_SESSID=f02644e00309751ddd2ca5ae444b70fd; path=/; HttpOnly
Transfer-Encoding: chunked
Content-Type: text/xml; charset=utf-8

<?xml version="1.0" encoding="utf-8" ?>
<result>
	<row>
		<idsite>1</idsite>
	</row>
</result>
Time: 0.08s

I hope you can help me to resolve this issue.
~ Jordh

https://wordpress.org/plugins/wp-piwik/