I had that happen with a reward points stay about three weeks ago.

The hotel said it was their second one of the day and blamed a new reservation system (I didn't get the full details but IHG is now using a range of numbers that weren't in place before and the system wasn't able to cope with it).

The reservation still showed in the app for me, so they found me a room. When checking out the next day, they also said that they'd contacted IHG and confirmed I had a valid reservation.

So everything got sorted apart from the stay hasn't posted against the Accelerate (the redeem your points offer).

Mine was a UK airport hotel outside London if you want to compare notes.