Whispers work perfectly fine for some older apps, and ones that are considered ‘safe’ and not spam bots. Whispers are also an allowed usage of chat by 3rd party developers, so the technical documentation for their usage is correct. Even if Twitch did add something to the docs, it likely couldn’t be anything more than “Some whispers may be restricted due to anti-spam measures”, as they are not going to go into anything more specific than that, so it wouldn’t be the most helpful of warnings anyway, and wouldn’t give any developer any clue as it if they will be impacted or not.
Twitch continuously change and adjust their spam protection as needed, so what may impact a whisper being valid or not could be true one day, and not the next. There’s also likely a large range of metrics involved to determine a bots ‘score’ and if their whispers are classed as spam or not, so even if a user sending a whisper first to the bot impacts whispers it likely isn’t the only thing and so could be misleading to mention some measures but not mention specifics or list it all, causing more confusion.