Database First Entity Framework Update Model is not working: What can be the reason?

This is the normal behavior. ;-)

Your conceptual model will not change if you just modify something DB side, even if you perform the "Update model from database" wizard. Please have a look at this SO answer where I explain how an EDMX is built and how it should evolve.

Check List

• Check Output window for any error occurred during command Update model from database
• Check your database connection string from .edmx property window
• Any custom code generation template that's causing it?
• Backup a copy of your .edmx, then try removing the modified entity from .edmx and re-add it back