After index disapear from serp . Why ?

Two page of my website after request to index in GSC show in serp for several hours then disapeare . Its 3 month old post.
What you think ?
I check keyword suffering and simillar post but has no problem

Your website pages disappearing from the search engine results page (SERP) after a few hours could be due to not being fully indexed or technical issues.

Possible reasons are:

Pages not fully indexed in search engines, which can take time even after submitting for indexing in Google Search Console. Check the indexing status in the Coverage report.
Pages not optimized for relevant and specific keywords your target audience is searching for.
Technical issues such as broken links, duplicate content, or incorrect canonical tags affecting visibility in search results. Regularly audit your website to fix issues.
Pages not having enough high-quality backlinks, which is an important ranking factor. Monitor performance and optimize for better visibility.