We recently updated a server that was using an older version of WinSCP. Server team made sure newest WinSCP was installed. Once the server was in production, we noticed the automated file transfers failing when a size threshold was hit. After several interactive verifications, we found this to be consistent behavior. All the logs seem to indicate the far side decides the activity has timed out and closes the operation. Restart(s) of download will eventually get the rest of the file.
After much effort, multiple machines, and OS versions, found that using 5.15.9 downloaded as expected. Versions above that had this same issue. I'm guessing it has to do with our outside source but was looking for some understanding of what might have changed or what might need to be reconfigured.
Tested versions: 5.15.5 ✔, 5.15.9 ✔, 5.17.0 ❌, 5.17.6 ❌, 5.19.7 ❌, 5.21.0 ❌