Bad parameter sniffing.
http://sqlinthewild.co.za/index.php/2007/11/27/parameter-sniffing/
https://www.simple-talk.com/sql/t-sql-programming/parameter-sniffing/
Or maybe stale stats.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability