The fault did not occur again (two days of downloading) and there is a fair chance it was an operator error (=me): as the files are quite large, the unit of file size does not always display on the window (MB or GB). So the "very large, merged files" may have been partially downloaded files and not merged files. Unfortunately I cannot go back in time to check.
For now, this post can be closed.
Thanks for the support

Normal logging level might be enough for start.

What debug level is suggested? I've selected Debug level 2 and the log file is 9GB is size (uncompressed). The fault has not occurred yet

Please attach a full session log file showing the problem (using the latest version of WinSCP).

Name the files that are merged.

Hi there,
I am using WinSCP 5.19.1 and have found at times that multiple files are merged into one file on downloading.
WinSCP is running on a Windows 10.0.17763 VM and connecting to a remote site. The connection is done using SCP. I am using the Commander interface style.
I am connecting to the VM using RDP and closing my RDP connection to let the download run in the background, if that makes any difference.
I select a number of files to transfer (~40) of which half are small (1kB) and the other half very large (70GB+). I select files from more than one folder and let them download in the background.
On more than one occasion the files were merged into a single file, while some on the same list are still separate. Is there a setting I can do to prevent this?
As the full download takes ~2 days, the link does disconnect briefly at times.
* I am also not able to resume a download. I am not sure if that is related.
Thanks for your help