Usually this would be due to the contract missing track details, if you scroll to the top of the contract to find the track listing there may be a red error message saying there are missing track details, you will then need to click on the track titles and complete any missing data before saving.
It's also possible the track details are totally missing, in which case there will be an 'Add Track' button at the top of the contract.
If neither of these help, please reach out to our support team.