On each subsequent sync WinSCP downloads each of the files again until the process reaches the "readonly files". At this point the sync fails.
Here is the scp script file, with server names removed.
option batch on
option confirm off
option syncdelete off
synchronize "LOCAL" "REMOTE"
IN the enviroment setting the Server Adjusts DST is set. New files arrive in the remote folder but none of the files change size or date - yet they are still downloaded every time.