I don’t work for Twitch and I can’t find any issue as it worked as expected for me during initial testing.
Whenever I send a message when banned I get the expected notice back when I have Tags and Commands Capabilities enabled.
My most recent tests have been using the Twitch Website itself.
And a token generated using the latest chat scopes.
And I have also tested using an ancient key on the old chat scopes. That seems to be where the fault is.
An oAuth generated using the deprecated scope of chat_login is not getting the notice. (Likely a spam counter measure but who knows)
This scope is also not even usable by “recently” create clientID’s so you shouldn’t be using it.
chat_login is (Deprecated — cannot be requested by new clients.) Log into chat and send messages.
Since the problem appears to be localized to the deprecated scope it’s unlike to be fixed as it works fine with chat:edit (for me at least) but I’ve observed a little inconsitency in my test accounts mix/matching mod/ban statuses here and there
End of the day the easiest way to see if you are banned, is to not send unsolicted messages in the first place (as your other posts suggest), or if you must check, open two connections to chat and see if your message arrived or not. (But that doesn’t discount a send fail)
It’s possible if you have been detected as a spam bot, you are getting silent fails.