In Safari Netflix video webpage, two fingers on trackpad causes unwanted zoom and hiding of text and Netflix control icons.

When I use two fingers on the trackpad of my early 2015 MacBook (MacOS 10.13.2), webpages in Safari will properly scroll but for one (known) exception: Netflix video. In a Netflix video screen, those two fingers on the trackpad in any direction cause text and icons in the Netflix control bar to shrink until they disappear, requiring reloading of the page. Netflix pages that are not video properly scroll. YouTube video is likewise unaffected. This anomaly started a few weeks after upgrading to High Sierra. This symptom only effects one user. When logged in as a test user, there is no such symptom.

So far with hours of guidance Apple Support assistance over several days: diagnoses run with no reported problems; Safari history cleared; trackpad and zoom settings checked; all Safari preferences checked; MacOS High Sierra reinstalled; plug-ins checked; MacOS and Safari preferences adjusted ad infinitum; hardware OK. (I've probably forgotten a few efforts.)

How do I return the trackpad to proper operation on Netflix video pages in Safari, and stop the trackpad from interfering with Netflix video controls?