Acronis Backup 11.5, Backup job doesn't finish the entire directory

Hello,
This is a new issue and recently it happend only to one main directory/folder which is located in the File server that runs Windows 2008, Enterprise edition SP2, 32bit.

I have 5 main folders which each shared folder contains many subfolders and individual files/documents of different file formats in a File server. Started 3 weeks ago, the backup job of one of the main shared folders didn’t back up the entire contents of the folder; it backed up subfolders up to the subfolders that its name started with "N" , and skipped the rest of the subfolders until it reached the individual files/documents, at that point the backup job started again to back up the individual documents.
In summary, I don’t have a complete backup of one out of 5 main folders. It starts from the beginning of subfolders but stops at subfolder that its name starts with letter "N", and then it skipped all subfolders to the end of the list of subfolders. When it reach the individuel documents, the job starts backing up the individual files/documents.
I know it sounds strange, for this reason, I setup a 3tb external HDD to make sure that storage size wasn’t an issue, to no avail. In addition, no exclusion in the Backup job has been created.
If you have any idea, I appreciated to share with me.
thank you