What causes ranking fluctuation ?

As i am newly working on a automotive site and published few pages in last week of august and maintained consistent backlinks out of which the results were up positive on ahrefs

10 keywords for 2 url reached under 9 position in mid month of september

Now past a month they are back to 21

What could have gone wrong ?

-added few blogs
-added few products during this period

few things I can think of...

- the site is fresh and hasn't won google's trust yet, so when you get links that can move the needle google will dance you until they figure out where to settle you;

- google update (sites don't usually dance during google updates, but on rare occasions they do);

- keyword cannibalization (if you have 2 or more pages targeting the same keyword(s), or keyword(s) with similar intent, all of those pages can go up and down the SERPs for weeks)

It sounds like you’ve made good progress with your automotive site, but the drop in rankings could be due to several factors. One possibility is that there may have been an algorithm update from Google that affected your site. Additionally, your competitors might have improved their SEO, which could push your site down in rankings. Changes you made, like adding new blogs or products, could also have altered keyword relevancy or diluted the focus of your pages. Lastly, the quality of your backlinks is important; if they changed during this period, it might impact your rankings as well.

Rankings fluctuate when pages are newly indexed because Google is still figuring out where they belong. Also, adding blogs and products could change your site structure a bit, which might impact keyword relevance.

and if competitors got stronger backlinks, that might affect your position too.

I’d keep an eye on those pages, review internal linking, and stay consistent with your SEO efforts.

Monitor your site's changes closely, as fluctuations can happen; ensure your content remains high-quality, relevant and up to date,\ and check for any technical issues or algorithm updates.

First off, algorithm fluctuations or new competition might have pushed your rankings down. Happens a lot after initial gains. Also, if the backlinks aren’t from super relevant or authoritative sites, they might not be holding weight.