Technical issues in Heroes IV.

The problem is that the game itself has a certain lag. Although it was removed in later versions, it still manifests itself to some extent - if you play for a long time, the game starts to slow down slightly - as if fatigue accumulates. And no memory cleanup helps - you have to restart the game.
Although, on the other hand, there is a certain plus to this (although I didn't think about it before) - the computer kind of reminds you that it's time to stop playing and take a break.