1. Google Algorithm Updates

Google continually improves the algorithm through regular updates for the purpose of upgrading the search results quality; thus, if your website fails to comply with the changes, it ends up losing its rank. Algorithm updates usually address concerns such as a deficiency in either the quality of content or the authenticity of backlinks; again, those that have failed to meet this evolving standard will most probably be faced with a conspicuous drop in visibility. 

2. Loss in Backlinks

They are one of the most important ranking factors in SEO because they speak for authority and trustworthiness. If important backlinks are lost due to link deletion or closure of a website, the rank of your site will drop. It will reduce your domain authority and make it harder to compete for the best positions in the search results.

3. Criteria for Technical SEO Issues

A good cause of slow page speed is crawl errors and sometimes even broken links, which impact a significant level of organic traffic to your website. These errors deny the search engines the crawling through to your pages, even the indexing of them, for which the site won't actually be indexed properly, leading to loss in inaccessibility and, therefore, traffic for you.

4. Decline in Content Quality

Search engines always value content that is productive and resourceful to users. Thus, if your content becomes out-of-date or irrelevant or even less comprehensive in comparison with what your competitors offer, then your rank definitely suffers. Well, the quality of content has an effect on SEO, of course, but it goes beyond just SEO because it involves a drop in user engagement and also trust in your website.

5. Improvements by Competitors

Your competitors are spending their time on SEO improvements, which causes them to outrank you. They might be publishing better content, getting more backlinks, or ranking for more trending keywords. Therefore, with their increased visibility, you will find the site losing part of its organic traffic.

6. Inefficient Keyword Strategy

Keywords form the basis of SEO; however, with targeting bad keywords, irrelevant or out-of-date, the site's visibility will not be too good. Also, not optimising for those long-tail keywords or some local searches can deprive you of this good traffic. Search trends always tend to evolve, so sticking with an old-keyword strategy leaves your future bright.

7. Problem for Mobile Friendliness 

Now, with most online searches being done via mobile, having a mobile-friendly website is inescapable. Failure to perform well on the mobile devices would result in higher bounce rates and eventually poor rankings. Search engines have mobile usability as a very stringent yardstick for their algorithms.

8.  Penalty Imposing by Search Engines

Penalties are one of those things that are able to flatten your rankings if search engine guidelines have to be broken. Keyword stuffing, duplication of content, or black-hat SEO practices may all invoke penalties. Sometimes, such violations may be inadvertent but can still affect traffic adversely.

9. Fluctuating Market Trends or Seasonality

Some businesses may undergo dynamic fluctuations in demand depending on the seasons or trends of the industry. If your site is heavily dependent on a specific time of the year, your traffic should be marked down during the off-season. Market fluctuations or changes in consumer behaviour can also affect search volume and web visits. 

10. Issues Arising from Migration or Redesign of the Site 

When website redesigns are done or websites migrate, most often the design is marred by a few technical glitches such as broken URLs, wrong redirects, and missing pages. Such errors would lead to confusion by search engines as well as users and may lead to lower ranking as well as organic traffic.

Diagnosing and Repairing a Drop in Traffic

First, do not panic when you notice a fall in organic traffic; rather, start by diagnosing the problem following these steps: 

• Analyse Traffic Sources: Use Google Analytics to pinpoint the affected pages, keywords, and timeframes.

• Audit Your Website: Conduct a technical SEO audit for crawl errors, slow load times, and other issues.

• Check for Penalties: Search for warnings in Google Search Console indicating penalties or indexing issues.

• Monitor Competitors: Check if it was because they published better, more relevant content that these competitors ranked better than you. 

• Examine Backlink Health: Use backlink analysis tools to check for lost or toxic links.