Installed 15.1.7 Hotfix 4 (15.1.7.267) yesterday and have had lots of problems with users uploading files that either get corrupted or in most cases the files are zero bytes.
You can replicate this situation as follows..
1. Update to Hotfix 4 (15.1.7.267)
2. Connect to serv-u in FileZilla, for example.
2. Upload around 100 files to the FTP server running serv u
4. Refresh the remote directory
5. You will see random 0 byte files that will say in serv-u they were "received successfully" but are 0 bytes.
This also happens in some cases to large files and they get corrupt / end mid-transfer.
Rolling back to Version 15.1.7.238 (15.1.7 Hotfix 3) resolves the issue so this is a problem with Hotfix 4.
I have replicated this on a fresh server with a trial and installed each hotfix in order.