Could be many different things causing this. First & formeost is its health, like: respiratory infection, mites, etc....
Other factors could be, but not limited to:
Caging conditions, like: temperature decrease, humidity, etc...
Brumation
Too large of a prey. (Even though it may have eaten that size before.)
Or, several other things.
Do a health inspection if you haven't already and double check caging conditions. Try feeding smaller live prey. If a snake is healthy, smaller live prey can sometimes induce feeding.
Is it active, compared to the other one?
Keep us posted & have a good one!
Mike
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It is said that 1 out of every 4 people are mentally unbalanced. Think of your 3 closest friends, if they're normal, then it's you.