This happens fairly frequently. Please see an answer from Phillip1 below that addresses this problem.
Rent is taxable in the year that the money is received (assuming that you are a cash basis taxpayer). Since the payment was not received until 2018, the money is not taxable until 2018.
- Include the full 1099-MISC in your rental income, and in the list of miscellaneous deductions add a deduction that is labeled "Rental income received in 2018".
- Keep detailed records for the receipt of your rental income that substantiates the fact that the payment was received after the 12/31/17
