Problem to connect with Serv-U FTP Server v15.1

Hi
We have been using software to connect to FTP servers for several years. Recently, we encountered a problem to connect with Serv-U FTP Server v15.1. After checking and searching on google, we found that most users using WinSCP have problems connecting to the mentioned FTP server. If possible, check the issue and provide a suitable solution.
Meanwhile, we were able to connect to Serv-U FTP Server v15.1 with VanDyke software.

Thanks for your report.
I have tested latest version of WinSCP (5.21.5) against the latest version of Serv-U FTP server (15.3.1), and did not have any problems. The server has only default settings. I've only added one test account.
Can you try the latest versions?