Thanks for the reply Martin, but I suspect I may have fixed the problem.
Whilst looking at the logs I had created, I realised I had set this particular system to use a network share directory for the local directory. I changed that to a directory on the local hard drive, and it has now gone 24hrs without missing a transfer. It would seem that there may be a problem with using a network share drive for the local directory when trying to keep a remote directory up to date.

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

I have 5 HP thin clients, each running an instance of WinSCP. 4 of them work exactly as they should, one does not.
They all also run an instance of MMSSTV (ham radio slow scan tv software) and each time a new picture is received WinSCP uploads it across my network to my web server.
The instance in question will initially scan the directory and then upload any new files it finds- after that it is pot luck whether it bothers to upload any new ones. Mostly it just sits there telling me "Change in Y directory detected" but not doing anything about it.
All 5 systems use the same version of Windows 7 embedded, and as far as I can tell, all are set up exactly the same. To complicate matters, just occasionally it will continue to upload new pictures as they come in for a while before then reverting to ignoring any new ones.
In all 5 instances WinSCP is version 5.21.5 (Build 12858 2022-10-06)
Any thoughts or suggestions gratefully received!
Ken, vk7krj
vk7krj.com