HoMM3 HD bug reports.

Recently, I've been encountering situations (though only with new players, ones I haven't played with before) where the opponent, after joining my hosted game, gets stuck while receiving the map headers and can't select a town. I initially thought the problem was a weak connection between the host and the joining player, but now I'm starting to doubt that. Especially since, in most cases, I can successfully join and everything works fine. So, what could be the real reason?