Inconsistent report distribution in recipient folder

[dafnis14]

Hi,

I have defined a task for an Excel report with a pivot table (very significant fact).

I have also defined a distribution to recipients folders:

According to filters which were applied, there were 4 folders created for recipients with the same report.

For one recipient, the date in the report  is occasionally displayed as a number instead of the expected format (DD/MM/YYYY):

This happens every other day and for the same one recipient only.

What might cause this issue?

Thanks!