The Airbnb information regarding taxes in Connecticut says: taxes are charged for the first 30 nights of a reservation. Simulating a booking on your listing shows me taxes increase for bookings up to 30 nights, but for longer stays taxes stay on the 30 nights amount. So this seems right to me.
I believe that they have paid tax now for 90 days, not the 30. I'm wondering whom to contact for this as a question to resolve as the renter would like to stay longer but this is affecting the decision.