FileZilla Server refusing connection - 425 error

I've looked at some other questions (for example, this one) but haven't found an answer there. Вот проблема:

I'm running FileZilla Server (0.9.60) on a server on our network. We have an external server trying to connect by FTPS. The connection has been working for several years, until a week ago. Now the server can connect and log in, but can't put the file. Here's a sample of what the log says:

(000080) 11/2/2017 3:30:01 AM - (not logged in) (XXX.XXX.XXX.XXX)> Connected on port 990, sending welcome message...
(000080) 11/2/2017 3:30:01 AM - (not logged in) (XXX.XXX.XXX.XXX)> 220-FileZilla Server 0.9.60 beta
(000080) 11/2/2017 3:30:01 AM - (not logged in) (XXX.XXX.XXX.XXX)> 220 You have connected to the RAI FTP server.
(000080) 11/2/2017 3:30:02 AM - (not logged in) (XXX.XXX.XXX.XXX)> TLS connection established
(000080) 11/2/2017 3:30:02 AM - (not logged in) (XXX.XXX.XXX.XXX)> USER USERNAME
(000080) 11/2/2017 3:30:02 AM - (not logged in) (XXX.XXX.XXX.XXX)> 331 Password required for USERNAME
(000080) 11/2/2017 3:30:02 AM - (not logged in) (XXX.XXX.XXX.XXX)> PASS *******
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 230 Logged on
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> SYST
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 215 UNIX emulated by FileZilla
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> CWD /staging/
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 250 CWD successful. "/staging" is current directory.
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> TYPE A
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 200 Type set to A
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> PBSZ 0
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 200 PBSZ=0
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> PROT P
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 200 Protection level set to P
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> PASV
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 227 Entering Passive Mode (XXX,XXX,XXX,XXX,26,129)
(000080) 11/2/2017 3:30:02 AM - USERNAME (XXX.XXX.XXX.XXX)> STOR search_report_11012017.txt
(000080) 11/2/2017 3:30:12 AM - USERNAME (XXX.XXX.XXX.XXX)> 425 Can't open data connection for transfer of "/staging/search_report_11012017.txt"
(000080) 11/2/2017 3:30:32 AM - USERNAME (XXX.XXX.XXX.XXX)> TYPE A
(000080) 11/2/2017 3:30:32 AM - USERNAME (XXX.XXX.XXX.XXX)> 200 Type set to A
(000080) 11/2/2017 3:30:32 AM - USERNAME (XXX.XXX.XXX.XXX)> PASV
(000080) 11/2/2017 3:30:32 AM - USERNAME (XXX.XXX.XXX.XXX)> 227 Entering Passive Mode (XXX,XXX,XXX,XXX,24,88)
(000080) 11/2/2017 3:30:32 AM - USERNAME (XXX.XXX.XXX.XXX)> STOR RAD_Affil_DL_110217.txt
(000080) 11/2/2017 3:30:42 AM - USERNAME (XXX.XXX.XXX.XXX)> 425 Can't open data connection for transfer of "/staging/RAD_Affil_DL_110217.txt"
(000080) 11/2/2017 3:31:02 AM - USERNAME (XXX.XXX.XXX.XXX)> QUIT
(000080) 11/2/2017 3:31:02 AM - USERNAME (XXX.XXX.XXX.XXX)> 221 Goodbye
(000080) 11/2/2017 3:31:02 AM - USERNAME (XXX.XXX.XXX.XXX)> disconnected

Here are the passive mode settings:

Брандмауэр Windows включен и специально разрешает порты TCP 20,21,990,6000-7000. Мой системный администратор уверяет меня, что те же порты перенаправляются через корпоративный брандмауэр. Я не знаю о каких-либо изменениях сервера или брандмауэра за последнюю неделю или более. Администратор внешнего сервера также не знает о каких-либо изменениях на его стороне.

Дайте мне знать, какая другая информация будет полезна.