I have been searching around for a while trying to solve this problem, and I don’t believe this solution has been documented yet. I apologize if I am mistaken and someone else has already reported this.
In a recent project I have been working on for my company, I needed to use the “Excel Application Scope” to open up Excel and work with Smart View. Of course, there is a bug that prevents the Add-In from loading. Today while opening my program, Smart View was loaded. It was the very first thing I did. This made me realize that there is a pattern to why it fails to load.
What I discovered is that the “Excel Application Scope” activity utilizes opening up Excel with a running background process to load faster on subsequent runs. However, this causes those subsequent runs to not load Add-Ins. By adding in the “Kill Process” activity to terminate Excel before using “Excel Application Scope”, it guarantees that Excel needs to be started fresh, causing the Add-Ins to load correctly.
I hope this helps those who are also stuck!