Drag and drop files from server to NAS with winscp, files disappear from server

Drag and drop files from server to NAS with WinSCP and files disappear from server. If the file is small, it can be uploaded to NAS without any problem, while if the file is large it shows file upload failure. Most importantly, the original file on the server also disappears.

I am setting drag and drop transfer via options to download files to any destination (general directory, zip file, FTP, etc) via temp folder. The settings show that the file is first downloaded to the temp directory and then placed in the target. After clicking to toggle this setting, it allows dragging and dropping files from the server to the NAS personal space now though, however this may not be just downloading to the temp file, but cutting to the temp file? Because the original file on the server disappeared. If the file is small, then it can be uploaded to NAS without any problem, while when the file is large, it will show upload error and the source file cannot be found. And I can't find the disappeared server source file even if I go to the system temp folder.

Where did my files go?

How should I transfer server files to NAS safely, effectively and quickly?

Probably needs logs. But, are you sure the NAS storage is setup correctly? Wrong NAS storage settings / setup can cause files to disappear from itself.

Its difficult to say what's going on based on that post especially as you say original file disappears and that kind of suggests you have a bad NAS setup. But, you might be saying something different.

Where exactly are you dropping the files to? (what window/application)? Can you post a screenshot?