ASO Google Play

Hello Im working on android app about one years and It whose very successful years in my life. My first app hit 500 000 downloads. I know that Im not new in this business but sometimes I don't understand what wrong I'm doing. Example: after I launched my first app I started to work on other one another, It whose successful again as well, 100 000+ downloads. So I continue my work, because I found system, good keywords to my niche and made third one app, I don everything like in previous apps, keyword in name, then - and name, 5 times added keyword in nice description and launched my app, after 8 hours I found my app rank nice 30 place by my keyword, but next day I whose not able to find my app using this keyword then after week I found that my app is not using my keyboard and it doesn't rank so nice, instead it ranks not good because it use bad keywords. So I continue my work and made another app, this one whose again successful hit 100 000 downloads.

So my question to people how it is possible? Or google doing something, or what? The same keyword, same system, nice future and screens, nice icons, everything nice, but app after few hours don't use main keyword, I even tried to add only keyword to my name.

Yes everything same. Why weird thing.

Even more stuff happening this month we lost all ranks in app. 50 main keywords just disappeared, app daily installs dropped from 7-8k to 600...