Thanks for the tips.

Memory pressure,

The server has 32GB of RAM, 28GB is assigned to SQL server as MAX memory. TempDB is presized to 10GB (app vendor best prac). The user DB that is hosted on the server is 48GB, the tempdb grew in about 3 minutes from 10GB to 20GB filling the disk. It would have to be an aweful lot of memory pressure to make SQL release 20 odd GB of memory to tempdb wouldn't it? Yes this server is excluive to SQL so SQL should only be competeing with Windows services for resources.

As for stats, the vendor gave us some update stats jobs that run every morning before the core userbase arrives. there is also a job that runs every hour that updates stats on some heavy hit tables. indexs are also rebuilt nightly.

All Jobs are from app vendor.

So what does this leave as likely outcomes?