As with everything, it can break from time to time, and with that endpoint being undocumented it should be expected to break/change/stop working at any point (although with the number of 3rd party services reliant on that endpoint I don’t see major changes to it any time soon.) and not rely on it for important functionality (such as determining if someone has the rights to use a certain command).
Look at the userstate object that is sent with messages, that will let you know if the user is a mod or broadcaster, so you can use that to determine if the bot should perform the command or not even if the chatters endpoint is having issues.