https://social.technet.microsoft.com/Forums/en-US/8f78bbe7-d8fc-4f61-8804-71b2abab547b/which-sql-maintenance-jobs-should-be-run-for-sharepoint-2013-databases?forum=sharepointadmin
Here is the solution the engineer gave us and which worked for us in all our SP2013 farms for all the affected content databases:
On the SQL server, you need to run update statistics and update execution plan for all SharePointDBs
Exec sp_MSForEachtable 'UPDATE STATISTICS WITH FULLSCAN'
DBCC FREEPROCCACHE
Exec sp_MSForEachtable 'UPDATE STATISTICS WITH FULLSCAN'
DBCC FREEPROCCACHE
