Certain file not fully uploaded

I use WinSCP to upload files generated by application chmProcessor to the WEB server. Very often it happens that all files are uploaded (files+directories selected locally) well except file jquery.layout-latest.min.js (resides at directory js). The file is shorter at the destination directory. When I repeat the upload of this file only it is then fully transferred.

WinSCP 5.13.4
Protocol FTP, port 21
Local machine:
OS Name: Microsoft Windows 10 Pro
OS Version: 10.0.17134 N/A Build 17134
Remote machine reports: HTTP Server: Apache/2.4.10 (Debian)

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

Good morning
I use WinSCP for transfering files to various websites I manage, without any trouble for months.
I recently changed my Internet connection from ADLS to Fiber Optics.
I now face incomplete transfers of large files, e.g. this morning a 6.5Mb file was not correctly transfered. I tried to transfer it again to another location of the same site, and that time it was correct. In both cases the size of the remote file was the same as the local file, so there was no evidence that is has been truncated, but as the format of that file is specific to a web application, I asked the support of the application provider who detected the incompleteness of that file.

The wrong version of the file is available at <invalid hyperlink removed by admin>, the right one at <invalid hyperlink removed by admin>

@PapyJP: Those links point to web pages. I'm not sure what to download. Can you post links to actual files?
Also you wrote that the files have the same size after upload. So what do you actually mean by claiming the files were "truncated"?

Today file jquery.jstree.js was not fully uploaded. The correct size is 179563 but only 147456 was uploaded. I attach the log.

@hynek: Do you have an access to FTP server log?

Unfortunately I do not.

How often does the problem occur?

Hi,
I assume I got the same Issue. Sometimes files are uploaded incompletely.
For example file 03.jpg has a size of 53.248 Bytes, after seemingly successful upload, size on the FTP-server is only 49152 bytes. After some investigation using wireshark it seems that WinSCP actually finishes the transfer after 49152 bytes (see attached screenshot). Could there be some internal error with handling files? Using Process Monitor it seems the local file is read in 4 batches and WinSCP somehow forgets about the last one (see other screenshot).
This was done using an older version of WinSCP and winscpnet.dll but the problem also occurs with the latest version and when starting the upload from the UI.

@martin.jakob: Can you send me an email, so I can send you back a debug version of WinSCP to track the problem? Please include link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.

Just sent you an email, thanks for your efforts

To detect that "Certain file not fully uploaded", I started to use Synchronize. I have to run it sometimes a few times till all files are same.

I believe I also spot a problem, when there files at the remote directory having the same but case-insensitive name. Supposed there are files A.txt and a.txt at remote folder but only A.txt at local one, the Synchronize seems like synchronizing local A.txt against remote a.txt which never succeeds...

I had the exact same problem. Pretty long. Only today I solved the problem. And the problem was antivirus Eset Smart Security. I deleted it (disabling does not help). You may have the same problem.

@Alexx: Thanks for your response. Eset antivirus could actually be the problem, since it is installed on all the affected systems.

I have the problem only when uploading to one server, so I believe the Eset is not the cause of the problem.

I thought so too. There are no patterns, they are loaded on the same with an error. On the other without. Remove, check. It will take no more than 10 minutes, but so many problems were solved at once.