Vector Parameter in Dynamic Material Instance not updating properly

Development Programming & Scripting Blueprint
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I’m making a game where the player character wears glasses that are affected by the world (steaming up in a warm room, getting rained on etc.) and I haven’t been able to get the material working properly. Everything looks like it’s set up properly, but knowing my luck it’s probably a single tick box I’ve missed. Can anyone spot what’s wrong here?

A demonstration of the fog effect not working (I used an image of Garfield for better visibility while testing). It should be adjusting the vertical offset and transparency every time I press up or down (shown by the print string from the below function)

The character blueprint that changes the parameter and prints the updated value. Value R changes the transparency of the fog (0-1) and value B changes the Y UV offset. I have triple-checked that the parameter name is correct and that the correct values are being changed.
The character blueprint that changes the parameter and prints the updated value. Value R changes the transparency of the fog (0-1) and value B changes the Y UV offset. I have triple-checked that the parameter name is correct and that the correct values are being changed.1587×537 108 KB

From the construction script of the character blueprint, the dynamic mat instance should be set up and stored as a variable
From the construction script of the character blueprint, the dynamic mat instance should be set up and stored as a variable989×347 50.9 KB

The material blueprint, as well as a demonstration of the parameter functioning properly in the editor