No data available for 3/6 months and 1 year intervals

I have two DS18B20 connected to my RPi-3 with Cayenne; I use these sensors to monitor the temperatures of two experiments I setup about 1 year later and until some days ago I was able to display data from both of them for all available intervals (real-time, hour, day, week, and so on).
From about a week I noted that data older than 1 month seem to be not available anymore; if I try to display graphs of both temperatures by the app and/or by CayExcel, I always obtain the “no data available for this period” warning.
If I access my dashboard by PC with Firefox, the same problem arise also when I choose to display data for a custom period and this is longer than one month.
Please can I know if this is a recent issue or modification to terms of use of Cayenne?

We have updated the data history period and only data for one month is shown.