You can make reservations at as many different hotels as you like. None should be cancelled by IHG or the individual hotel. There are many valid reasons for wanting two hotels for the same day, although you rarely receive points and elite status credit for more than one property per night.

Airlines are different. Automatic cancellation of double bookings on the same flight are common. I'm rather surprised to see the cancellation of a booking on a different flight though - it's fairly reasonable for a business traveler to hold a seat on more than one plane to ensure that they can travel. I've had award bookings on the same day to different destinations, with no problems.