@Cronus-Z
Interesting! What is surprising is that there is nothing major changed in search in 7.1 Could you let us know from which version you upgraded?
Would it be possible for you to enable slow queries on your database, and log the exact query that is being slow? The “cancelling statement due to user request” just means that the query has taken more than SqlSettings.QueryTimeout value to execute and the application has cancelled the query.
What we’d need to do is bump up the query timeout to prevent the application cancelling it, and therefore let it appear in the slow query logs.
Once we have the exact SQL query, we can run some debugging on that to see what is in the query that is causing the CPU spikes.