Decrease in the position of the new page – what happened?
If, as you say, the site is new and there is no suspiciously large number of incoming links yet, it may be the so-called. Fresh Site Bonus, something like a search engine bonus to get you started :). For several weeks, the site is high in search results, then falls into positions for no apparent reason, which Google deems appropriate for her.
On the other hand, if you have exaggerated with the number of links leading to your website, it could in fact endanger her seriously and a filter might have been applied, which sometimes comes across newly indexed pages. It is for a specific keyword and can be imposed for several weeks, months, and even half a year. That's why cautious linking is so important for new sites, too many links in a short period of time can bring more losses than gains.