Version 3.49-2 (httrack_x64-noinst-3.49.2)
GUI interface (WinHTTrack.exe)
Windows 10 Pro x86_64 with NTFS

I'm sorry for causing a potential confusion in my previous post.

Because I'm using a 64-bit OS and 64-bit version of HTTrack, I have no
problems with downloading files greater than 4 GB in size while mirroring
sites via HTTrack. Though I prefer to cancel downloading files if they are
greater than 1 GB and download them with another download-manager and copy
them into their mirrored location, IF ONLY these >1 GB files won't get
finished downloading when I'm not available (sleeping, out, etc.). However
this last sentence has nothing to do with this subject.

Anyway, I have no problems with HTTrack downloading files greater than 4 GB,
due to OS and HTTrack being 64-bit architecture.

However, as per your original concern, upon using the action "* Update
existing download", regardless of the sizes of previously completed
(downloaded) (by HTTrack) files, HTTrack somehow resets them and starts to
download them AGAIN. This is the issue I face and mentioned previously as "it
is exactly the same on WinHTTrack 3.49-2 on Windows x86-64".

Because of the OS and HTTrack arch.s I use, I'll fail to contribute to your
issue in the manner of file sizes greater than 4 GB. But I confirm, for "*
Update existing download" action, my HTTrack redownloads all files.

All in all, HTTrack community clearly posts issues they face. I'm sure when
developers have time, these issues will either get solved or marked as "no
solution". ;)