I've had stays fail to post a couple of times. From what I remember, the issue was that if the eligible spend is higher than the total billed, it will not post. This can happen if the hotel charges you for something that they are not supposed to, and then instead of removing it, they enter a negative charge to offset it. The system will flag it and not post it. It will need manual intervention; someone will need to clean up the folio.

I've never seen anything post with the wrong number of nights. Usually when people complain about this it's because they don't understand that on an nth night free rate (3rd night free, 4th night free, whatever) the free night is not an EQN.