We’ve found that a Google Ads account suddenly taking a downturn in performance is very rare …but it’s not unheard of. What to do when performance tanks in PPC on Search Engine Land is a decent guide to the steps that can be taken to investigate, if the worst happens.
The article suggests that the Change History Report is the first port of call – has something in the account been changed, possibly without the knowledge of the person responsible? It also suggests checking the site for changes, such as tags being removed. We’ve seen this a number of times.
Other things to investigate include competitor activity, external events and seasonality. Best of luck!