Nothing has to be wrong, Google's decision to show featured snippets can change based on data not directly related to your site.

Judging from the Semrush Sensor data, Featured Snippets are now shown for <5% of (tracked) queries vs. 6% in August.

The drop continues for us and we are losing several FS everyday. The drop is gradual and we are not sure about how we can still show at position 1 and no longer trigger a FS. That started happening mid-july and I couldn't find any relevant update regarding this situation.

Featured snippets show the best answer to an informational query from pages where the page title may not convey it answers the query. If you tweak the titles of too many pages in a short period of time you'll find you may lose ALL of your featured snippets at once.

As for FS vs #1 - The featured snippet sits atop the SERP while #1, on a page where Video replaces the FS location, may be sitting a screen below the fold.

Short of creating a video to retain the traffic for informational queries there's not much you can do. Thing is, creating a video doesn't bring your site any direct traffic so you're working on your brand on someone else's domain.

I understand but pages having the same title are generating FS and I had FS for more than 2 years with the same titles. I still retain the NO.1 position but just not a FS. I'm trying to dig more into this.

No. I'm not trying to revise the page titles as that doesn't make sense. I'm just digging more.

Some articles get many of them, others get none, it's all about how well a paragraph of yours answers a query which has a FS box above results.

For starters check to see if the keywords/phrases a page ranks for even have an FS associated with them, most keywords/phrases do not. Next evaluate if your page can answer the query in a concise manner better than the currently chosen FS. Next consider the difficulty of the keyword, if there is lots of competition for the keyword it's likely there will be for the FS as well.

Ranking an entire page for the #1 spot has no effect on whether or not that page gets the FS and It may actually hinder your efforts as you can't have both spots.

Recently the number of queries having a FS has gone down, often replaced with a videos box it seems, so if your FS of two years was one of them it no longer exists.

Word of caution - if you write a page full of FS queries as header tags and try to get the snippet for each the page likely won't do very well, it's not written for humans. Be mindful of whats atop the SERP for the topic you're writing about but focus on page quality, the snippets will take care of themselves(if there are any left)

What niche is your site in? If you're in the firearms, fireworks, gambling, tobacco, vape, or a few others, featured snippets have been removed. You would still have some from articles and such but if you had any products or categories attached in this niche, you very well may have lost them that way.