The most common failure mode would probably be a failure to successfully parse some of the code input into it. This would lead to a lower integrity and usefulness of the database as a whole. This could be remedied with better use of grammars, tokenizers, and parsers
The second most common service failure would be a failure of the API key authentication system.This would either allow someone access to something they shouldn't have or deny someone access to their own repository. This can be remedied by a simple reset / redistribution of the user's / organization's API keys
Lastly, the third most common failure mode would be loss of data through database or network failure. This, fortunately, can sometimes be remedied by keeping backups and using drive recovery services
The last kind of failure mode would be user error. Either they fail to corectly add a databse or they fail to correctly install the system. This would likely result in total failure of the system as a whole. Luckily, provided the user didn't delete the original data, they should be able to be helped by customer support personnel.