If you notice your chat messages show up in the chat feed but don't appear on the streamers in-screen chat, you have been shadowbanned.

Twitch will still take your money for donations, subs, etc, but your feedback won't be seen by anybody but you. This shadowban does not appear in the appeals page and can be applied randomly and intermittently. You are never informed about this by the way. You'll likely be talking in a chat and assuming you're being ignored. Hop into a private tab and load up the stream where you'll be able to notice if your messages are missing in chat.

From my observations, there seems to be some type of algorithm/system that determines who to shadowban. I'm assuming it assigns extra points for factors like VPN usage, Linux, and adblockers. Once you've been shadowbanned, switching one of those three will not work to unban you until some arbitrary timer expires.

I'm posting this in case anybody else has experienced this and felt frustrated and isolated. You're not being ignored (unless you're a twat and are being ignored). You're just being punished by Twitch for being privacy conscious.