FileZilla Server keeps repeating file (receive) transfers and never completes

[DTMT]

Hi,

We are using FileZilla Server to handle a number of offsite backup transfers from backups at other sites. This has always worked very well for us. The system running the FileZilla server directs the files to shares on a NAS.

Recently, I am having an issue (and only with new file transfer setups; that is, we create a new ftp user, set up a folder on the NAS, and assign permissions so that user will be directed there when files are received) where the files start to transfer, hit 100%, then aren't found; FileZilla deletes the .tmp file that is part of the transfer, and disconnects the user, whereupon the next time the user connects, wash, rinse, repeat. Here is an example from the log statement (IP address and username have been sanitized). Older clients are transferring files just fine, only new ones have been a problem. Also, very small files seem to go fine; larger files seem to have the issue.

I have tried the following:

1. Upgraded FileZilla Server (now running 0.9.60 beta)
2. Reset the passwords of the users in question (we use 12-character alphanumeric with capitals, no symbols to ensure UTF-8 compatibility)
3. Gone through all the settings of our backup client that performs the FTP to the FileZilla Server and confirmed they are correct.
4. Restarted our NAS, after upgrading its OS (Synology Rackstation)
5. Restarted our FileZilla Server (running Server 2008 R2, up-to-date on patches).

Here is the log snippet. If anyone could provide assistance, I would greatly appreciate it. I can provide additional logging on request.

(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 230 Logged on
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> TYPE I
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 200 Type set to I
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> PWD
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 257 "/" is current directory.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000523) 4/26/2018 0:02:05 AM - cigftp84 (96.75.44.137)> disconnected.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> PWD
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 257 "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> SIZE C_VOL-b001.spk
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 213 512
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> SIZE C_VOL-b001.md5
(000543) 4/26/2018 0:02:05 AM - userlogin001 (192.168.1.1)> 213 82
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> CWD /BACKUPFOLDER-01
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 250 CWD successful. "/BACKUPFOLDER-01" is current directory.
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> SIZE C_VOL-b001.spf
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 550 File not found
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> SIZE C_VOL-b001.spf.tmp
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 213 2767781888
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> SIZE C_VOL-b001.spf.tmp
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 213 2767781888
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> PASV
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 227 Entering Passive Mode (192,168,254,165,195,127)
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> REST 2767781888
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 350 Rest supported. Restarting at 2767781888
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> DELE C_VOL-b001.spf.tmp
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> 250 File deleted successfully
(000543) 4/26/2018 0:02:06 AM - userlogin001 (192.168.1.1)> disconnected.

[botg]

The log does not even show a transfer attempt. The temporary file is deleted because the client told FileZilla Server to delete it.