Sorry for "necroing" such an old thread. But figure i'd provide you guys and anyone else with a possible fix on this. I had the same issue and realized that it was after I setup ELS that it started happening. The AI would drive perfectly fine chasing them from a distance but when I got up on their tail and changed siren tones they would stop steering and immediately crash. I went in the ELS .ini file and turned the two lines below to "false". This seemed to fix it so far, I will come back and edit it if i'm incorrect. I only tried on a few different callouts.
ElsActiveOnAi = false
ElsTrafCtrlOn = false
I don't notice a difference with traffic control turned off. AI still yield the same way.