Article Pages disapear on the google website

I am running a Joomla website and trying to get a better position on google by writing articles. The problem is that the articles are indexed and come up to the first or second pages of google in a month but they disappear suddenly. Besides that, the google search console shows everything is good and indexed well. Even when I type site:mysite.com I can find some of the articles which are indexed but are not shown in the even 10 first pages of google.
Please if you have knowledge of this problem, contact me.