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

For a long time, I've been suffering from the random repositioning of hero icons in the corresponding menu (to the left of the castles). The main hero might be at the top, but after I take my turn, he's at the bottom. I know about the Alt key shortcut, which allows me to move the hero back to the top, but he can still slide down again.
I used to play at 800x600 for a long time, and I thought it was a problem with the old interface. I switched to 830x664, and it's the same.
It seems like a small thing, but it's incredibly annoying.

In the original game, the hero slides down after being moved to and from the city's garrison. When a hero is moved to the garrison, he is removed from the list of external heroes. There can be 8 external heroes and 48 garrisoned heroes.
When a hero is moved back from the garrison, there is no way to know what his previous position in the list was, especially since other heroes may also enter or leave the garrisons between the time he is placed in the garrison and when he is moved back. Therefore, when a hero is moved from the garrison back to the map, he is added to the list as the last one.

I am not aware of any cases of a hero spontaneously moving around the list without being placed in the garrison.