Maintenance Plan with performance poor after

Hello, Guys!

I've one instance with 19 databases and its use is 473 GB.

Every day we execute the follow points:
- Reorganize or Rebuild Indexes;
- Update Statistics (sp_updatestats);
- Recompile Procedures;

We've one problem in some days, because some procedures after execute the job for rebulid and update stats, your performance is poor.

When I look the plan is poor the posterior day.
The solution occurs when I execute the update stats again.

Why occurs this problem? 

What's the better moment to update my statistics in your opinion?

Thanks!

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Vithor da Silva e Silva | MCTS - SQL Server 2008, Implementation and Maintenance Site: http://www.vssti.com.br Blog: http://vssti.blogspot.com