Not found: Table seraphic-plexus-404015: (Bigquery)

Question

Why does the same code work sometimes and doesn't others? Is it because I am using sandbox?

Here is the code:

SELECT 
  * 
FROM 
  `seraphic-plexus-404015.employee_data.departments ` 

I opened new query in a new tab and it didn't work, the FROM kept raising an error that the table can't be found But i opened a query from the table when it was open and it worked Here is the code:

SELECT 
  *
FROM
  `seraphic-plexus-404015.employee_data.departments`