Bing Deindexation Case Study: How We Lost Rankings (3rd Time)

Last Thursday, August 28, 2025, our website was deindexed by Bing Search for the third time—here's a record of what happened. The root cause was likely that changes I thought were minor actually appeared to search engines as site-wide modifications. Consider this a cautionary tale.

On the previous day (August 27), I checked my Ahrefs score and noticed a surge in "HTML language mismatch" errors, as shown in the image below around August 24. We had recently started implementing multilingual support across the site, but I hadn’t realized that the HTML language tags were being dynamically set based on user preferences. From Bing’s perspective, all language versions were being identified as my fallback language (even Chinese articles had an "en" language tag). During those days, I repeatedly changed the language setting back and forth—zh → en → zh → en—multiple times within a few days.

Around August 26, I performed a full content replacement across articles, removing some notices I deemed unnecessary, and failed to use search engine submission tools.

On August 27, I completely rewrote the navigation pages to better support multiple languages. I discovered that the meta descriptions for English pages were entirely in Chinese—likely an oversight on my part—so I deleted all English meta descriptions with the intention of rewriting them later.

On the night before August 28, I had a cup of milk tea and woke up around 5 a.m. the next day. Since I was already up early, I fixed the HTML lang issues. I posted updates, refreshed downloads, and began setting up database caching, planning to soon separate APIs across multiple sites so yinyuee.com could have independent login and download features.

By around 3:30 p.m., I was nearly done. I checked my phone and noticed that no one had followed our WeChat official account since about 2 p.m.—a sudden drop. I wondered if the website server had crashed or if the redirect server was down. After a quick check, everything seemed fine. I tested logging in and downloading content myself—everything worked normally. Then I checked Baidu Analytics...

Hmm. I searched for our site and found it wasn’t appearing in results at all. Many of my keywords had been ranking on the first page, daily clicks were nearing a thousand, and daily WeChat followers were steadily increasing—then it all stopped abruptly. As shown below, most impressions came from 360 Secure Browser and 360 Safeguard, but there were zero actual clicks on these keywords.

Of course, these are just what I believe to be the main contributing factors. There were actually several other issues—here’s a brief list:

1. robots.txt had errors
   I considered robots.txt a minor issue, but the bigger problem is that Bing and Yandex share some technical infrastructure and data—they tend to block sites simultaneously.
   I verified my site with Yandex on August 24. Then, on Thursday, August 28 at 14:12, Yandex sent me an email:

   

2. Sitemap was incorrect
   Due to a misconfigured environment variable during submission, the sitemap generated pointed to changjiu365.cn—a domain that had been blocked months earlier. I had noticed this issue before but hadn’t taken it seriously.

   

3. Frequent site-wide changes
   At the end of July, I made another major overhaul. Since then, Google Search Console has been unable to crawl or update indexed URLs. It wasn’t until today (September 4) that it recovered—likely after a month-long observation period.

   

   

I’ve gradually fixed these issues over the past few days. So now, it’s time to start over once again~