I try to download myst3v122patch.exe from demos.residualvm.org (http://demos.residualvm.org/patches/myst3v122patch.exe)
but get an error:

The connection to the server was reset while the page was loading.

All other Myst3 patches can be downloaded successfully.

What is the problem with myst3v122patch.exe?
Can you fix it?

I've been able to download that file just fine.
Are you sure you are not using some proxy server / antivirus which would prevent the download of that executable file?

Yes, you are right: my Antivirus program (Avast) sees it as Win32:Malware-gen.
Do you know why this is?

By the way, excluding both the URL and the bin directory of MYST III from Avast makes it work.

This is a false positive.
Though VirusTotal gives a ratio of 10/54.
Maybe we should consider providing the patch already extracted, without the installer.

Be aware that Avast is also triggered by the extracted file M3.exe and considers it malware.
Therefore only delivering the extracts does not solve this problem, at least if you are using Avast.

M3.exe has a ratio of 11/57.

Ok, thanks for sharing. Then I guess there is nothing we can do.