First is that UTH on a tstat? If not, it needs to be. They can burn, kill, your snake.
You say mouse. Does that mean a fuzzy?
Usually when a person says mouse they mean a mature one.....that is where my mind goes.
How did you heat it?
I thaw mine in warm water and then do a water change once thawed with hot tap water to serve them. I serve them wet. A mouse body temp is slightly over 100F so the feeder needs to be near the same for the best results....especially going from live to f/t.