Backup over FTP gets stuck at 99%

[i80r]

Hi everyone!

Recently I've stumbled upon a strange behavior of the backup process over FTP. When backing up from GAIA the process gets stuck at 99%. Now there seem to be solutions for it already like sk118752  and sk100403. However, the provided solutions only interrupt the current backup process in my case. When starting the backup over the same thing happens once again.

Further investigation displayed that backup files are getting fully transmitted at around 36% and after that the connection from checkpoint is closed and nothing is transmitted to the server.

FTP Server Log:

(000061)26.08.2021 17:05:31 - checkpoint > 230 Logged on
(000061)26.08.2021 17:05:31 - checkpoint > TYPE I
(000061)26.08.2021 17:05:31 - checkpoint > 200 Type set to I
(000061)26.08.2021 17:05:31 - checkpoint > CWD /xxx/
(000061)26.08.2021 17:05:31 - checkpoint > 250 CWD successful. "/xxx" is current directory.
(000061)26.08.2021 17:05:31 - checkpoint > PASV
(000061)26.08.2021 17:05:31 - checkpoint > 227 Entering Passive Mode
(000061)26.08.2021 17:05:31 - checkpoint > STOR backup_KMG-5900-SG2.kmg.kz_26_Aug_2021_17_04_50.tgz
(000061)26.08.2021 17:05:31 - checkpoint > 150 Opening data channel for file upload to server of "/xxx/yyy.tgz"
(000061)26.08.2021 17:06:30 - checkpoint > 226 Successfully transferred "/xxx/yyy.tgz"
(000061)26.08.2021 17:06:49 - checkpoint > disconnected.

Other appliances in the same network behave correctly.

Has anyone had the same problem or where do I start debugging on the checkpoint?