Blitter Unable to be Activated At Runtime

I have a system right now that should allow me to use post-processing effects/materials on the UI, but it's giving me some issues. For one, while materials loaded and active from the start of the program are applied with no problems at all, it is impossible to activate it at an arbitrary point after starting the game. I have tried switching the material used in the blitter, using the same material constantly but keeping its values at 0 until needed, and a few other things, but nothing is able to get the glitter to apply the material unless it is active and applied from the moment I hit Play. What might I be able to do to fix this issue?