Excellent product! I have a small bug report.
In your iOS app, the modification dates for some files are displayed as "(null)" in table view. For example, instead of "548 KB - 31 Jul 2017, 11:24" that lower line will show "548 KB - (null)".
I've confirmed that the modification dates are preserved properly in the cloud storage provider (Box in my case) and also in your desktop app. Whether a date is displayed properly seems to depend purely on the date itself! Some modification dates will display properly, others will not.
For example, if I take a file whose date is displayed as "(null)" in the iOS app, and change the modification date manually in the desktop app (by copying the file from Boxcryptor into an offline directory, changing the modification with "touch -m -t XXXX [filename]", and placing that file back in Boxcryptor), its date will then display properly in the iOS app (if the new date is one which displays properly). This also works in reverse - if I take a file whose date is displaying properly, manually change the date to a problematic date, and re-upload, the modification date for the newly uploaded file will be displayed as "(null)".
I don't know exactly which dates don't display properly but the morning of July 31 was consistently causing problems.