Which endpoints? I haven't had any problems accessing match endpoints in the last 24 hours.
Bug? code 0

Got this again. This time it was misspelt team name.
I am now fairly sure this is being returned in some instances instead of a 404 response.
"404 =
we try to tell you if the URL is malformed or the data requested is just not available (e.g., a username for a user that does not exist)"

Thanks for responding. I understand you are V busy ATM
I think it is any unknown username or club name. It used to return a 404 and now sends back the code 0 internal error. Try this.
https://api.chess.com/pub/player/ed_shirley
This used to be a valid username but think it got re-named.

It fails with error 0 in the https://api.chess.com/pub/tournament/{id} for me.

It's most likely because the member closed their account, or had it closed for fair play, abuse. Type: ed_shirley or another banned or closed account, and you will see that there is no profile available for them. Because of this, it makes sense that you aren't getting anything for endpoints for a closed account.
Got this response code a few times last few days.
{"code":0,"message":"An internal error has occurred. Please contact Chess.com Developer's Forum for further help https://www.chess.com/club/chess-com-developer-community ."}
anyone else?