Delay when changing background in slide master

Hi all! I'm having the following issue and wanted to see if any of you had a similar problem before. 

 

What I want to achieve:

I'm building a game. At the beginning, the user has to select an "scenario" in which the game will take place. The background then remains the same until the end of the game, so I built it in the slide master.

 

What I have now:

This triggers actually work, but I have a problem I'll explain later on. What I have now is: The background is constructed in the slide master, and has different images in states (an office, a lab, a factory). Then, I have three triggers set like this (one per state): "Change state of "background" to "lab" when timeline starts in this slide if variable "scenario" equals to "1".

In a regular slide, the variable scenario changes to "1, 2 or 3" when the user clicks on one of the three scenarios. 

 

The problem:

This work! But I have a substantial problem: The trigger that changes the background "when timeline starts" has a bit of a delay, so every time the user jumps from one slide to another they can see for a second the background in "normal" state and then it changes to the scenario the user has chosen. This is a pain point in the experience as it seems like a glitch. I also noticed that if the slide has a transition, the background image doesn't change until the transition is over, which makes the glitch even more noticeable. 

 

I tried:

- Lowering the images quality to see if that was causing the delay (It didn't work).

 

I would like to avoid:

- Triplicate every slide and redirect the user to one path or another depending on their choice. 

 

Do you guys have any idea on how to solve this? 

Thank you a lot!