It sounds like you might be encountering a few potential issues here. While broad match keywords can capture a wide range of searches, a couple of factors could be affecting your impressions:
1. **Low Search Volume:** Even broad match keywords can have low search volume if they are too niche. Google might categorize some keywords as not having enough search activity to trigger ads.
2. **Bidding Strategy Change:** Switching from “max clicks” to “max conversions” can also play a role in this. “Max conversions” relies on historical conversion data, and if there’s not enough data yet, Google might throttle impressions until the algorithm can learn more. This can especially affect broad match keywords that cast a wider net but don’t have much conversion history yet.
3. **Ad Group Structure:** If you have ad groups with only one broad match keyword, you might not be providing enough signals for Google to optimize and find related searches. Try expanding your keyword set or experimenting with different match types to see if that helps.
A possible solution would be to give the algorithm some time to gather data or try switching back to a more flexible bidding strategy (e.g., max clicks or target CPA) if the lack of impressions persists.
Hope this helps!