Maybe someone can offer some advice.

Why, when I click the surrender button with a hero, does the game freeze, but this only happens with one hero, while the others are fine?

For the Dark Elves, one of the heroes loses the visibility of their hero model on the map. If you remove that hero completely from the game, it causes problems; upon restarting, it switches to another hero. What can be done about this? (It doesn't matter if it's the standard hero model or a modified one).

Could these be heroes from the same mod?

In the first case, I can't help you; I don't know much about the mechanics of surrendering.

My only hypothesis is related to the TOWN_NO_TYPE faction. If a hero belongs to this faction, when they surrender, they should end up in a tavern with a level 1 unit, but neutral factions don't have level 1 units, which causes a bug (but this is a very specific case).

Does the hero's model not appear from the start, or does it disappear during the game?
Usually, when you remove a mod and load a save file that was created with that mod, its remnants can corrupt the game, or the opposite can happen: if you play as the Orc faction, save the game, and then install a mod for the Stronghold town, the Orc town will look like a terrible mess, the heroes will have old models, and the units may completely lose their models on the global map. This is a classic bug; the save file remembers which models were on the map and tries to load them into the game, even when they have been replaced or are missing