Da-KolkoZ downgraded by Google

The Da-KolkoZ blog has just been downgraded by Google.
According to my statistical tool, Da-KolkoZ recorded a spectacular drop of -86% of visits and page views compared to the previous day.
Apparently the problem has already affected many sites but no concrete explanation emerges from this observation.
Is this the Google Sandbox effect ?
However, no technical modification has been made for many weeks, the site does not present satellite pages, no illegal content, respects the Google charter, does not present hidden content, nor wild redirects.
The site is crawled almost every day, and features new content every day.
In short, I cannot explain this sudden loss of traffic; I contacted Google support in order to submit my problem to them, hoping that it will answer me and explain the cause of this problem to me quickly enough …
In the meantime, the KolkoZ continues its journey by offering you new news every day.