Scripts

It doesn't help; the problem remains the same – the task isn't failing, no one is losing, and the console isn't showing any errors.

I've conveyed the essence of the error – the function takes 4 parameters + there's an unnecessary check with an infinite loop. It's possible that the syntax is incorrect (I mentioned that I didn't check it in the game).
Try adding some "print" statements to see what the console shows.

...And the number 1, by the way, is because the task fails for the first player.

...The conditions: there's an elven town belonging to an elf (Player 3). If Player 2 captures it, the task fails, and Player 2 loses.

To avoid confusion, use constants – PLAYER_1, PLAYER_... etc. This is a good and established practice.
There weren't any such conditions, so I considered it an error, but it's not really important.

...You need to be more careful with variable names.

What do you mean? I don't see any differences. If you're talking about the style of writing variables, it doesn't matter (PascalCase or camelCase).