vsftpd "553: Could not create file" error (once in a while)

Hello,

We recently upgraded our server upgraded from 6.7 to 7.2(in-place upgrade) , since then we are getting 553: Could not create file(once in a while) if they retry it suddenly works. This would rule out any permission problems.

Here is the error message:
Tue Aug 1 23:15:42 2017 [pid 3] [ftpuser] FTP response: Client "x.x.x.x", "553 Could not create file."
Tue Aug 1 23:15:42 2017 [pid 3] [ftpuser] FAIL UPLOAD: Client "x.x.x.x", "/targetpath/logfile.txt", 0.00Kbyte/sec
Tue Aug 1 23:15:42 2017 [pid 3] [ftpuser] FTP command: Client ""x.x.x.x"", "QUIT"
Tue Aug 1 23:15:42 2017 [pid 3] [ftpuser] FTP response: Client ""x.x.x.x"", "221 Goodbye."

Is there somebody who could point me to a direction which I haven't investigated yet?
Thanks in advance for any help,

VSFTPD Version: 3.0.2

Thanks and Regards,
Prasad