I just experienced in my campaign upon resuming it from a save file the breaking of all of my military alliances. This also affected a number of, but not all, AI nations as well. I don't know what caused it but I do have a theory. My theory is that when a save is reloaded the game has to set the opinion modifiers between the nations and resets the personalities of the AI nations, leading to a mismatch of what existed before the same and what exists after the save so many of the alliances and other treaties break upon unpausing of the game. I did notice that when I loaded up the game the last time at a save, that the opinion modifiers changed when I opened the diplomatic panel while still paused. Its very weird and I'd like to hear of anybody else has experienced this.