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Alexa and DA are completely synthetic attempt by third-parties to try to guess what search engines might think of a website. Alexa, in particular, is a totally unreliable way of measuring the influence of most sites. If these measures have changed significantly, but with no change from your site's own data (e.g. Analytics, Search Console, careful rank testing etc) then it's far more likely that the third-party tools are having problems, not your site. Put another way - those third-party tools are hints. If they indicate potential problems, you'll need to assess actual website performance to determine if there's a real problem, or if the 3rd party tools are misreporting. Hope that makes sense? Paul