Question: Why would liquid half-and-half creamer curdle when poured into hot coffee? This happens to me sometimes, and I'm not sure why. Could it have something to do with either the coffee being too hot or the creamer being too cold?

Answer: 
I would think this is happening because your cream is just about to turn sour. 

As cream ages, lactic acid builds up in it. The acidity in your coffee is enough at that point to push the cream over the edge to curdling. 

Try newer cream or a very low-acid coffee with old cream and you should be OK.
I had this happen to me in the most bizarre circumstance. I buy green coffee beans and roast them myself at home. I have decaf and regular that I roasted separately, then grind them together to make half decaf and then brew my coffee via pour over ( no machines). I did this and then used soy creamer (brand new, not old). Didn't curdle. Then, I brewed a cup with just the regular beans (no decaf). Same way, same day, everything the same other than it was full caff. Added the same soy creamer and it curdled. I repeated this exactly the next day and it did it again!! My guess is it has to do with the acidity of the coffee beans.