Due to extremely heavy download volume, the log feature has been turned off for most files. You can find the number of visits to your shared folder, but not about how many downloads.
As a work around, you can monitor the network usage (download bytes in account balance) to check if anybody has accessed your files.
If you have a group account, you can share folders from different sub-accounts, you can then monitor the account balance to check if anybody has downloaded your files.