weird jump and drop in rank

2am, im trying to optimize my description by adding few keywords i found in similar apps description . it was kind of stuffed but i didnt receive any complains about that.(i got one but for another app where i put a word ‘keywords’ , so foolish of me). anyway my new app had some stagnation for few days, displaying at rank 80-90 on the most crucial keyword in search ranking. then after few minutes since i sent my new description my app is 15th. i was like wtf, checked few times. then after 10 minutes my app is down again at 90th. i tried to make my description less stuffy, I’ll report results after few hours. till then, can sb explain to me what the hell happened? was it good aso then penalty for stuffing keywords? im new to aso, just used my experience in seo.

ps: sry about my writing style, im using my cellphone now,its hard to type here

My impression is that Google sometimes changes the ranking algorithm. If I searched on a keyword for some of my apps, my app always was behind the same apps. Then, suddenly, the order changed completely, with other apps I had hardly noticed before, in front of my apps. Then, about a week later, the same old ranking appeared again. I think they use a lot of variables, and change the weights of them, which causes different outcomes. For instance, I have the impression that paid apps are placed more in front, and the higher the price, the higher the ranking. Because that’s profitable for Google. An other variable is the percentage of the keyword in the title. When I added another keyword in a title, my app ranked lower for the initial keyword, probably because there are more words that do not match the searchword.
Who knows more about the ranking algorithm?

ya keyword density always plays a role everywhere including websites, amazon listing and app stores.

thx for reply. i changed description again (deleted some part of it) and after few hours its 80th. i know that aso can change rank but i wasnt expecting going so high and then drop in the matter of minutes.