The error : The query has been cancelled because the estimated cost of this query (xxxx) exceeds the configured threshold of 600. Contact the system administrator
On our shared hosting servers we do not allow queries to exceed the limit of 600s or 10 mins.
Running queries longer than this can cause issues in a shared hosting environment. Queries that run longer than 600s is called "expensive queries" as per Microsoft.
Note on shared hosting we dont have 1 customer using our SQL server at any given time we have 100s hence its shared amongst users hence limits are in place to keep it stable and our business to continue to run.
If any customers require more than this you will require a VPS Server. We do offer Unmanaged Windows VPS servers where you could install SQL Server Express on it and hosts your DBs on top of that with your own settings you control. Alternatively you could move your website/s and databases and email to our Managed Plesk VPS servers where we can manage and adjust settings aswell to your requirements.
More information can be read here: https://docs.microsoft.com/en-us/sql/relational-databases/resource-governor/resource-governor?view=sql-server-ver15