Whenever a combat is starting, the game freezes for some time, usually 1 or 2 mn. If I click anywhere, Windows gives the "Close the program or wait for it to respond" message.
Interestingly enough, the freeze seems to occur exactly on my first character turn: if one of my characters has the best initiative score, the freeze happens immediately at the start of the combat ; all bad guys playing before my first character can run their turn normally.
The Same issue also happens at the end of the combat.
PS : just sent an email with my save file and more technical details