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.
The trouble with this unsupported endpoint is that there is no supported equivalent. This is bad news for loyalty bots and I do hope that Twitch are searching for a solution despite it being unsupported.
I experiment the same problem. A workaround could be using the notifications you get through the IRC chat. It’s not very accurate, but it works.
For my personnals needs, I manage my own user lists, and combine the informations (of the API and the IRC notifications) to be as accurate as possible.
I hope that the API will integrate an accurate list request one day.
Thanks for the suggestion. I do know that this workaround will only work in channels with less than 1000 viewers - once there is more than 1000 viewers, then only moderators are announced.