I uninstalled both The Contact Form and e-Newsletter plugins, but checking modsec logs I see many many 500 internal server errors related to these two plugins.
It mainly seems to be search engines that cannot find either plugin (because they are not there) but continue to search and trigger a rule preventing a lot of internal redirects.
Log sample of one event (there are a LOT more)
[12/Jan/2016:03:56:33 +0000] VpR5cVKlIywAAFXovWoAAAAO 126.96.36.199 42481 MY IP ADDRESS 443
GET //wp-content/plugins/e-newsletter/email-newsletter-files/js/widget_script.js HTTP/1.1
Host: MY DOMAIN
User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
HTTP/1.1 500 Internal Server Error
Content-Type: text/html; charset=iso-8859-1