Auto-name all chats only touches conversations that have never been given a name. If a chat already has a title, whether you typed it or an earlier run of auto-naming generated it, it is skipped and left exactly as it was. That is the whole rule, and it is why running it a second time appears to do nothing.
The option is under the three dot menu at the top of the chat.
Which chats it will rename
A chat qualifies only if its title is still one of these:
- New Chat
- Chat
- Empty
- Anything beginning with Chat - , which is the dated fallback name
And it must have at least one message in it. An empty conversation has nothing to build a name from and is passed over.
Everything else is treated as named. A chat auto-named last week now carries a real title, so the next run leaves it alone. That is deliberate: the alternative would be renaming your whole history every time you pressed it.
Why you get no feedback
The run reports nothing on screen. There is no message saying how many were renamed and none saying that nothing qualified, so pressing it on a fully named list looks identical to pressing it on a list of twenty untitled chats. Watch the chat list itself: names that were going to change have changed by the time the spinner stops.
How the name is chosen
The title is generated from the first three messages of the conversation, which is usually enough to capture what you were asking about. It works best on chats that get to the point early. A conversation that opened with "hi" and wandered for ten messages before arriving at the real question will get a title drawn from the greeting, not the question.
Renaming one chat yourself
Open the chat, then choose Edit Title from the same three dot menu. That works on any chat regardless of what it is currently called, and a title you set by hand is permanent as far as auto-naming is concerned: it will never be overwritten by a later run.
If you want a badly auto-named chat renamed properly, use Edit Title. Running Auto-name all chats again will not revisit it.
One neighbouring option to avoid
The same menu carries Clear all chats, which is not a renaming tool and removes conversations from your list. Do not reach for it while hunting for the naming option. What removal actually does is covered in deleting a chat.