The choices that other advertisers, who are participating in the same auctions as you, make can affect your campaign’s performance. New advertisers or advertisers who adjust their existing accounts can affect how many impressions your ads receive.
Example
Note: Merchants in CSS countries using more than one CSS may experience performance fluctuation between accounts for Performance Max and Shopping campaigns. This is because although multiple accounts are bidding, only one can win each auction.
For example, the performance of your campaign with CSS A could drop, while the performance of another of your campaign with CSS B targeting the same products could increase.
A merchant will never be second-priced against itself in the auction for any offer, and that rule holds irrespective of the number, or identity, of the CSSs used by the merchant. Learn more about auction dynamics between CSS.
What you can do
The Auction insights report lets you compare your performance with other advertisers who are participating in the same auctions that you are. This info can help you make decisions about your bidding and budget.
Impression share data, specifically Lost Search IS (ad rank), can help you identify the percentage of time that your ads weren't shown on the Search Network due to poor Ad Rank in the auction. In order to minimize Lost Search IS (ad rank), improve your ad quality and your bids.
Need something else?
Check other common reasons why your campaign performance is fluctuating.
