Random "ERROR_CANT_ACCESS_FILE [MoveFileEx]" during synchronization to local folder

[andreino]

Hi everyone,
I am experiencing an intermittent issue while syncing a network folder to a local folder.

Scenario:
Source: Network Share (UNC path/Mapped Drive)
Structure: The source files are located within subfolders that are Junction Points (not physical directories).
Destination: Local Drive
Permissions: Full read/write access on both ends. Manual file copying works perfectly without any errors, so NTFS permissions don't seem to be the culprit.

The Issue:
Step 1 (Compare): Works fine. It correctly identifies files to be deleted, updated, or copied.
Step 2 (Synchronize): This is where it fails randomly.
"Cannot rename [local_path\file_name.ffs_tmp] to [file_name.ext]. ERROR_CANT_ACCESS_FILE: The process cannot access the file because it is being used by another process. [MoveFileEx]"

Observations:
The error only happens when copying from the network to the local folder.
It is random: some files are copied successfully while others fail. Even if I run the compare and sync process again, the issue consistently occurs with the same specific files.
If I manually copy the exact same files using Windows Explorer, I encounter no issues.

It seems like the .ffs_tmp file is being "locked" immediately after creation, preventing the final rename.

System Info:
OS: Windows 10 with ESU activated
Software: FreeFileSync v14.8 64bit (but the error occours with older versions too)

Has anyone encountered this behavior before? Could it be an antivirus interference or a Windows Search Indexing issue? Any advice on how to prevent these temporary locks would be greatly appreciated.

[xCSxXenon]

My first thought was also some antivirus, especially if you are using 3rd party AV. Try with your AV disabled temporarily