Dynamic Material Alpha doesn't work

I’m trying to make a sphere that grows and becomes transparent over time until it reaches a certain radius. It should start as a small red ball and should end as a big almost-transparent red ball, but I’m having difficulty with the transparency. I’m creating a dynamic material based on a simple material with Base Color (1,0,0,1):

And this is the size and alpha logic:

Everything before SetActorScale3D is size related. To get the alpha, I’m lerping from 1 to 0.3. This is giving me the values I want, but in-game, my ball is always non-transparent, as if the alpha setted is being ignored.

Any thoughts about what is happening?