I played several minutes both on Firefox and Chome and still not able to reproduce the FPS drop.
I took a look at the visual scripts and didn't find anything that may cause FPS drop.
I was just walking in the maze, get the shield, and the orange button. Did you do something different when the FPS drop?
I recommend you open the bebug panel, and check the "object count", as shown in the image above. Is this "object count" increasing too much when the FPS drop? What is the "object count" when it happens?