HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Crash when taking a turn, although I suspect the reason was the second instance of the game running, although by that time I had already closed it, but I noticed that such things happen more often if 2 instances of the game are running.

To eliminate crashes related to this, you need to launch each instance of the game from its own folder (i.e., from different folders).
I did a lot to make it possible to play multiple games from one folder, but apparently, there are still problems.

Crash when viewing scrolls in the backpack and with Gunnara. The opponent wrote that it was at this time that the turn was passed.

Checked. Yes, it exists. If, while waiting for a turn, you view information about an artifact in the open backpack window, and at that time the opponent passes the turn, there will be a crash. I will try to fix this, but for now, keep this in mind...