Backup to ftp errror

I have migrated the WordPress server to a new server (Ubuntu 18.04 to 20.04). The whole setup was taken over. The backup ran on the old server without any problems. On the new server there is a problem with the upload to the ftp server:

WARNING: ftp_nb_fput(): php_connect_nonb() failed: Operation now in progress (115)

Here is log:

[09-Jul-2020 08:25:41] 1. Try to send backup file to an FTP server …
[09-Jul-2020 08:25:41] Connected via explicit SSL-FTP to server: ftp.server.com:21
[09-Jul-2020 08:25:41] FTP client command: USER UserName
[09-Jul-2020 08:25:41] FTP server response: User UserName logged in.
[09-Jul-2020 08:25:41] FTP client command: SYST
[09-Jul-2020 08:25:41] FTP server reply: UNIX
[09-Jul-2020 08:25:41] FTP current folder is: /users/UserName/tmp/
[09-Jul-2020 08:25:41] FTP client command: PASV
[09-Jul-2020 08:25:41] FTP server reply: Entering passive mode
[09-Jul-2020 08:25:41] Starting upload to FTP  …
[09-Jul-2020 08:27:11] WARNING: ftp_nb_fput(): php_connect_nonb() failed: Operation now in progress (115)
[09-Jul-2020 08:27:11] WARNING: ftp_nb_fput(): Entering Passive Mode (85,214,3,73,247,33).
[09-Jul-2020 08:27:11] ERROR: Cannot transfer backup to FTP server!
[09-Jul-2020 08:27:11] Restart after 91 seconds.
[09-Jul-2020 08:27:13] 2. Try to send backup file to an FTP server …
[09-Jul-2020 08:27:13] Connected via explicit SSL-FTP to server: ftp.server.com:21
[09-Jul-2020 08:27:13] FTP client command: USER UserName
[09-Jul-2020 08:27:13] FTP server response: User UserName logged in.
[09-Jul-2020 08:27:13] FTP client command: SYST
[09-Jul-2020 08:27:13] FTP server reply: UNIX
[09-Jul-2020 08:27:13] FTP current folder is: /users/UserName/tmp/
[09-Jul-2020 08:27:13] FTP client command: PASV
[09-Jul-2020 08:27:13] FTP server reply: Entering passive mode
[09-Jul-2020 08:27:13] Starting upload to FTP  …
[09-Jul-2020 08:28:43] WARNING: ftp_nb_fput(): php_connect_nonb() failed: Operation now in progress (115)
[09-Jul-2020 08:28:43] WARNING: ftp_nb_fput(): Entering Passive Mode (85,214,3,73,244,185).
[09-Jul-2020 08:28:43] ERROR: Cannot transfer backup to FTP server!
[09-Jul-2020 08:28:43] Restart after 91 seconds.
[09-Jul-2020 08:28:44] 3. Try to send backup file to an FTP server …
[09-Jul-2020 08:28:44] Connected via explicit SSL-FTP to server: ftp.server.com:21
[09-Jul-2020 08:28:44] FTP client command: USER UserName
[09-Jul-2020 08:28:44] FTP server response: User UserName logged in.
[09-Jul-2020 08:28:44] FTP client command: SYST
[09-Jul-2020 08:28:44] FTP server reply: UNIX
[09-Jul-2020 08:28:45] FTP current folder is: /users/UserName/tmp/
[09-Jul-2020 08:28:45] FTP client command: PASV
[09-Jul-2020 08:28:45] FTP server reply: Entering passive mode
[09-Jul-2020 08:28:45] Starting upload to FTP  …
[09-Jul-2020 08:30:15] WARNING: ftp_nb_fput(): php_connect_nonb() failed: Operation now in progress (115)
[09-Jul-2020 08:30:15] WARNING: ftp_nb_fput(): Entering Passive Mode (85,214,3,73,250,151).
[09-Jul-2020 08:30:15] ERROR: Cannot transfer backup to FTP server!
[09-Jul-2020 08:30:15] Restart after 91 seconds.
[09-Jul-2020 08:30:16] ERROR: Step aborted: too many attempts!
[09-Jul-2020 08:30:16] One old log deleted
[09-Jul-2020 08:30:16] ERROR: Job has ended with errors in 275 seconds. You must resolve the errors for correct execution.