The Nginx version that is bundled with Plesk is the very out-dated 1.11.1 (31 May 2016) and needs updating for fixes for vulnerability CVE-2017-7529 and a long list of bugs. See https://talk.plesk.com/forums/plesk-suggestions-and-feedback.676/create-thread
Recommended is updating to the latest stable (LTS) release: 1.12.2 (17 Oct 2017)
Recommended is updating to the latest stable (LTS) release: 1.12.2 (17 Oct 2017)