Previous month statistics disappeared

Goodmorning everyone. I’ve been in Piwik for about ten days. I did not have any particular problems. Today I checked the statistics and I saw that the statistics for the month of December 2017 have disappeared. Voluntarily I did not put any fla for the cancellation of reports or visits and logs. I wanted to check how much the database volume increased.
How is it possible?
I thank the collaboration in advance