The actor on begin is working correctly and triggers the blueprint correctly. The issue is with the comparison in the blueprint. It compares FirstPersonCharacter string against "FirstPersonCharacter_C_1" this is because the character is instanced in the real game and isn't instanced when running from the editor. You can test the blueprint using the print blueprint funciton.
When a project is packaged and has the 'event actoronbegin' within a blueprint, the 'event actoronbegin' no longer responds. It does respond within the Editor though.
Packaged Project: [Link Removed]
1. Download the Zipped Project or the Packaged Project from in the description.
2. If Downloading the Zipped Project, please open the project
3. Ensure the 'Pick Up' is placed inside of the level
4. Check the 'Pick Up' blueprint and ensure it's to 'FirstPersonCharacter' not 'ThirdPersonCharacter'
5. Package the Project and run the .exe
Expected: The material of the static mesh should change per the blueprint coding
Result: The material never changes upon collision
Head over to the existingAnswerHub thread and let us know what's up.