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

How do you know so much about me? ;)

We played together, don't you remember? :-)
Improved Gameplay was disabled. I personally enjoy playing with "pure SoD," but as practice shows, most of the bugs have already been fixed, although this wasn't explicitly stated. The problem isn't the patch itself, but rather the raw pseudocode generated by IDA. Editing it eliminates bugs because the crash log contains the necessary address. All changes always included messages indicating which bugs were disabled (marked like this: [-] Bug ...)

In other words, Improved Gameplay is specifically responsible for the bugs, so using certain bugs (like viewing other players' cities) won't cause any problems if you use them carefully. If you click on a second city during the opponent's turn, and they don't have that city, the game will crash, but otherwise, everything will be fine. The same applies to other bugs. However, when the game is played without bugs, the crash rate is extremely low. And most crashes are caused by bugs in the mod, not the game itself, which is a slightly different issue. ;-)
So, I recommend enabling IG. It's more stable to play without bugs, even if it's not what you're used to. I enjoyed it myself, but I played for a month without them, and it didn't seem that significant. There's a description on the website; if you read it, you can avoid some game crashes.
https://sites.google.com/site/heroes3hd/description3
It's all explained clearly.