Reply To: Mix Shader not working for 2nd node tree (Using B 2.90.0)
Well, it looks like you have two Mapping Nodes on top of each other in the bottom part of your tree:
The top one, that is visible has the keyframes, bot no input in the Vector socket, so in stead of using the Object Coordinates, it just uses one point:0, 0, 0), So everything that comes after that Mapping Node is being calculated in that single point. Hence the single color on frame 251.
I hope that helps.