I discovered this a couple of weeks ago, but it just hit me again this morning.
I have a number of materials that depend on Material Parameter Collections. These were all working fine, but then I went and added another parameter to the Collection.
Suddenly my Materials weren’t properly pulling the values from the Collection, even though all of the parameters I was using were still there. I had to go into the Material, move a node slightly to flag it as dirty, and then click “Apply” to get my changes to properly come through when doing a PIE.
I get that the shader needs to be recompiled, but could this not be done automatically?