We show Google AI Overview as “no results” for some prompts because Google decides on a case-by-case basis whether to display it. It’s completely normal for AI Overviews to appear inconsistently across different days. This isn’t something to worry about, and we have no way to control when it appears.
You can confirm this by searching the same prompt on different browsers or devices. You may see the AI Overview appear on some but not on others.
