When changing the key interpolation of a material curve in an animation to constant it appears to break the updating of the material after the changes are applied. Until the changes are applied it appears to be working as intended.
Regression: Yes, this appears to have been working in the 4.21.2 - 4753657 release version of the engine
Result: The Cube stops changing colors
Expected: The cube would continue to change colors due to the change in the scalar parameter that is used in the mesh's material
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-75453 in the post.