Carnival Spirit at times may be "Out Of Range" - Online vessel tracking relies on the use of Automatic Identification System (AIS) data. Most modern vessels even today still use VHF, line-of-sight equipment, to transmit their AIS data. This line of sight limitation will require even the tallest of vessels to be within approximately 100 miles of shore in order for the data to be received. Newer satellite relay services are available but at a very high cost. The land based VHF relaying still remains a free service for all vessels which is why it is still popular today.
Although I can't say for certain, I believe this was more than likely the issue. The ship was out of reporting range at the time you were trying to track it. This is not unusual especially for the longer Carnival Spirit cruises which spend a lot of time out of range while cruising to remote Pacific Islands.
