Dear Nikos,
This is because ESA changed few weeks ago the online products retention policy (the interval for how long the products are kept into the online archive) from 1 year to only 1 month 
, according to this:
https://scihub.copernicus.eu/twiki/do/view/SciHubUserGuide/LongTermArchive#Online_Products_Retention_Policy
Best regards,
Cosmin