If your server is not communicating with WinSCP, it's not WinSCP error. If you have problems with the connecting getting stalled temporarily, you can set a longer timeout to avoid seeing the message.

Hello,

The "host is not communicating" error is getting very annoying, can you fix it once and for all? It pops up randomly every now and then.

It's been reported so many times since 2011:
https://www.google.com/?q="host+is+not+communicating+for+more+than+15+seconds"
and still nobody knows how to solve that frustrating issue.

Optimizing the buffer as suggested does not help.

Thank you

PS: SFTP connection, logged in as root via ssh keys, /bin/bash, port 22xxx