I can give you more information about this issue:
The encrypted files with date of 03/April/2017, are unencrypted correctly.
But the files that I am unable to unencrypt has the followig date: 04 october 2013.
For sure these files has been encrypted also on 03/April/2017. So I dont understand why they have that date, but something is hhapenning with this files, I can not unencrypt them