I can't connect using the HD mod.
I have the exact same problem. I spent a lot of time on it, and not just my own, but also the time of the helpful people here (a separate thank you to them). But I still haven't solved the problem. So that others don't waste their time, I'll list what definitely DOESN'T help:
1. Disabling all firewalls and antivirus programs.
2. Setting up Hamachi and network priorities.
3. Installing a VPN version of TeamViewer.
4. Downloading various "correct" versions of Heroes with and without the mod pre-installed.
5. Changing computers (!).
6. Changing the connection location.
What I was able to determine: it connects with some people, but not with most. What it depends on – I don't know. Without the mod, it connects with everyone. The VT version connects with everyone.
The fact that the HD mod affects the connection is 100%, because without it, everything works, and without any complicated procedures. I contacted Baratortch in a private message and on the forum, but apparently, the number of my posts on the forum is not enough to get a response