I’m not sure whether the small green “(1)” at the top left in this screenshot is meant to replace the header indicator. Since there hasn’t been any update here, I’m unsure, but it feels like this might be the replacement, so I thought this could be the right place for feedback.
In some cases, switching chats when a new message arrives probably makes sense. It becomes confusing, though, when the new message is in the same chat you’re currently reading.
I often scroll up to read older messages (for example, when preparing a reply). In that situation, the indicator makes me click the arrow, which takes me out of the chat, even though the new message is actually there. At least in my experience, the person I’m actively chatting with is more likely to respond than someone else, so leaving the chat feels unnecessary. In this case, it would be more intuitive if the indicator guided me to use the bottom arrow to scroll to the new message, rather than the left arrow that switches chats.