Hello–this is a common issue that comes up on the forums, and I want to point you all to a few resources. First of all, we have a fairly extensive discussion on Secret Recovery Phrases (seed phrases) here. Second, we have a dedicated Knowledge Base article specifically on this topic.
Lastly, I want to point you to a forum discussion on this topic which should serve as the definitive response in this regard: Restored Metamask No coins are showing - #107 by jacob.cantele