Unless you make more assumptions about the truth value of the messages, say 'one message is false' you can't draw a logical conclusion.
If, for example only one message is false then as you said message 2 and 3 are contradictory and so if message 2 is false, the treasure is in box 3, if message 3 is false, the treasure is in box 2. Here you see that the assumption 'one message is false' still doesn't provide enough information to draw a conclusion. For that you'd need a more specific assumption like 'message 1 and 2 are right'.
Just given the messages with no information and let all be true gives a contradiction and the treasure could be everywhere. Or nowhere.