Let us explain the reason:
When Thirtyseven4 scans any archive file types (zip, rar, etc.), the scanner first extracts the files in the TEMP folder for scanning purpose and deletes it once the scanning of that file is finished. The process goes like this -> Extract - Scan - Delete for each file present in the archive. During the delete operation, we have observed that sometimes Thirtyseven4 fails to delete the temp files because the file is accessed by another Windows processes/services or any other third party application like monitoring/backup software.
Fix:
Open your Thirtyseven4 Console webpage > go to Settings > Scan Settings > bottom of this page there is an option to 'Exclude Files & Folders'. Click the Add button and add the C:/Program Files/Thirtyseven4/Thirtyseven4/Temp path.
Hit the 'Save Policy' button towards the bottom of the page.