Have you given airbnb a call?
Possibly issues with the payment, it takes a bit of time to clear properly so if there was an issue the guest hasn't mentioned airbnb may have cancelled it.
Other than funds not cleared, there are a whole bunch of reasons with payment, maybe detected fraud activity, maybe using a payment method attached to another account with issues breaking the rules somewhere.
If thats the case i'd be wary of the guest 'offering' to pay cash on arrival to 'sort the problem out easily betweeb the two of you'.
It could be somthing totally innocent, but airbnb should be able to tell you a bit of info first.