This is Auction Overlap

Auction Overlap occurs when multiple ad sets target the same audience and try to enter the same auction on Facebook. Facebook's algorithm will select the ad with the highest total value, which is determined by bid, estimated action rates, and ad quality. The selected ad enters the auction, while the others are not considered. This mechanism is designed to prevent advertisers from competing against themselves.

Auction Overlap is most likely to happen when you have multiple ad sets targeting the same people. To prevent Auction Overlap, you should:

• Limit the number of competing ad sets that target the same audience.
• Be cautious with features like Advantage+ Audience and Advantage audience expansion, as they can inadvertently create overlapping audiences.
• Follow Meta's guidance to limit the number of unnecessary ad sets, which can lead to more efficient ad performance.

You should consider combining ad sets when Auction Overlap becomes an issue and you see Delivery Recommendations suggesting to do so. This can help in reducing competition between your own ad sets and may lead to more stable and predictable ad performance, especially when scaling.

To manage Auction Overlap, you can create an Automated Rule that either:

• Dynamically combines ad sets when overlap is detected, or
• Sends an alert to notify you of Auction Overlap, giving you the option to manually combine ad sets or take other appropriate actions.

Avoiding Auction Overlap is important when scaling because too much overlap can lead to higher costs, under delivery, and less stable and predictable performance. It may also make it more difficult to exit the Learning Phase of an ad campaign, which is crucial for optimizing ad performance.