This does not seem to be related to a host key.
WinSCP log file indicates that the server has closed the connection.
If both sides believe that the other side has closed the connection, it can be due to the network or a firewall.
Can you connect with any other SSH/SFTP client?

Currently running winscp version 5.17 on a windows box (10? maybe) to connect via sftp to a Moveit DMZ server. The server where winscp is installed is a cloud hosted server that I do not have access to perse - my access if via screenshare where I walk someone through manually clicking and typing. Things were running smoothly for years until changes were made to up the security on the Moveit Server side. It appears the host key changed with the updated settings but instead of being prompted when connecting after the settings were changed the winscp client connection window just closes with the message that "remote site unexpectedly closed network connection". The Moveit log seems to indicate that it is the client initiating the close and I suspect it's an issue with that host key. How might I update that key manually or rule that potential issue out altogether? I can manually install Moveit on any of my machines and connect without issue using the same version with all the same settings. The primary difference being that any new install I use simply asks me to accept the host key without issue. I opened a ticket with the host to be sure port 22 was open - they say it is and the moveit log showing the attempted connection seems to verify that. Any help is appreciated.