Please attach a full log file showing the problem.
I have struggled a bit with an issue where winscp continues downloading a file forever, even though the size is suddenly bigger than the file on the server.
It happens if you download something from a server which doesn't support the REST feature, but you stated -resume in the winscp get command. If the connection breaks during the download and it tries to resume you get the situation where the file keeps growing. Perhaps the client should only resume a file if the server supports it.