If there’s a sudden drop or increase in global pings or tag fires for a conversion action that your campaign is using for Autobidding, this can result in a drop in serving and spending as Google Ads optimizes towards your set conversion action.
If you’re looking at conversion-related metrics like cost/conversion over recent date ranges, be sure to consider conversion lag (also known as "conversion delay").
Example
What you can do
For campaign types where it’s available, Explanations will highlight conversion delay as a root cause in scenarios where it detects a high degree of lag based on historical conversion data given the selected date range.
Use the conversion lag report to understand conversion delay information on key metrics, such as cost-per-acquisition (CPA) or return-on-ad-spend (ROAS). These are used to predict how actual CPA or ROAS values may change once adjusted for conversion lag.
Need something else?
Check other common reasons why your campaign performance is fluctuating.
