We had an issue with our booking details - so we could not complete the check-in online. It took 4 days to get a sufficient response from the hotel, including being given wrong numbers in London and Rome. In the end, we got a response that resolved the issue 1 hour AFTER we were due to check-in!
Hugely stressful considering we were travelling from Italy and didn't know whether we would be able to access our room when we arrived.
To add insult to injury, it turns out there was a person at a reception all along that could have just checked us in when we got there. A complete joke!