I would like to help troubleshoot for you. Can you share your recipe with us? What kind of egg whites are you using (from a carton, from shelled eggs, Eggology)? What kind/brand of butter? What speed on your KA is it when you add the hot sugar syrup (and what temp are you cooking the syrup to?) and what do you turn it down to after all the syrup is added? Is this the same speed when you add the butter?
When I have failures with IMBC, it's usually when the syrup is added (the whites collapse). It normally goes to "soup" when some amount of butter is added, then it comes together (emulsifies). Sometimes if it hasn't emulsified by the time I've added most of the butter, I just stop and let it beat (with the whip) for a minute or two and it comes together enough so I can continue adding the remaining butter.
