Some reasons why your Google Ranking Changes
First of all, I would like to mention that Google’s algorithm update and development method has changed. Google followed a method of extracting certain updates for specific areas over the years. Lately this method has been replaced by bulk kernel updates. The impact of mobile usage priorities and rapid change in Web technologies is also very big. This has caused the effects to become too large. While webmasters could easily observe these effects for themselves, the only thing that changed in terms of users was that more user-friendly pages were displayed on the Google search results page.

Check Order Tracking Method
If your client is running the ranking tracking from the Google search results page, it should be explained that this is the wrong method. The Google algorithms are enough for each user to have different conditions, so that a page appears in different order to the user.
Check for Recent Changes
If you receive a mail titled that our website will continue to work with the most up-to-date technology tomorrow after the software update is done tonight, you may not know that the website is temporarily receiving noindex tags for only a few hours of work. Worst of all, it may be even worse that the small tag is forgotten there after the update.
Check Backlink
A large number of recent link losses can trigger a decline in your traffic, which may be reflected in ranking performance. Sometimes Webmasters who have migrated to Https and who forget to redirect or forget to redirect the URL structure and cause redirection can trigger these link losses.
Check Security Status
Sometimes even the most secure systems can be captured, misused. Such events will adversely affect your ranking performance. Beyond standard safety procedures, controls that provide extra protection can save lives. If you are faced with the ever-deteriorating ranking performance beyond variability, it is better to have a professional security check.