Site affected by Google's Helpful Content updates?

  One way to try to identify whether your review-type content has been affected by Google's "helpful content" updates or related Core Updates is to look at your Search Console traffic / impressions etc for review-type searches bring traffic to review content pages in relation to when these updates were introduced. This is part of a holistic "process of elimination" to rule out all other possible causes such as seasonality, backlinks, changes to the SERP / search behaviour, negative SEO, Google penalties etc (this is not an exhaustive list).

   See https://developers.google.com/search/updates/core-updates / https://developers.google.com/search/docs/fundamentals/creating-helpful-content . For review type content guidance see https://developers.google.com/search/docs/specialty/ecommerce/write-high-quality-reviews . 

   Note that the “position difference” number below indicates the number of rankings positions dropped.