So, I found a few similar topics but none of the proposed solutions seemed to work in my case, then I decided to create a separate topic hoping this time I can get some help. 
Basically, after the execution of a macro, several sheets of the workbook are populated with data and some specific cells are referenced by formulas. Some of these formulas contain functions that depend on Add-Ins to work correctly. When I open the workbook by hand or using the Start Process activity I am able to get the correct value for the cell. The same does not happen when I use Excel Application Scope: and the cell gets the value “#NAME?” since the Add-In wasn’t loaded, therefore the function wasn’t recognized.
What I can do: use Start Process, use Ctrl + G to go to each cell, copy the cell content and use the clipboard value in my automation. But that seems tricky and not reliable.
What I want to do: use Start Process and then reference this already opened workbook using Excel Scope Activity, and get the cell value using Read Cell activity.
But when I try to do this the Excel Scope Activity opens the same workbook again without the Add-Ins loaded and getting the wrong value. Is it possible to use Excel Application Scope to reference a workbook previously opened using Start Process? Or is there any other way to load Add-Ins?