A Microsoft service that provides website owners with tools to monitor, analyze, and optimize their site's performance in Bing search results.
Noted. For situations like this, the correct next step is to submit a request directly to the Bing Webmaster team so they can review the domain internally.
You can raise a support request here: https://www.bing.com/webmasters/support
Select Indexing as the issue type and include your domain, sitemap URL, and a brief explanation that the site disappeared from Bing results while remaining indexed in Google.
If Bing Webmaster Tools is connected, it also helps to include screenshots of the Index Coverage / Pages discovered graph and the Sitemaps status, as this can help their team identify whether the crawler stopped processing the domain.
Once submitted, the Bing Webmaster team will be able to check the indexing status and let you know if there is a specific reason the site was removed from the index.