The Time material node returns editor up-time instead of game time if the material is set to the material domain User Interface.

Development Rendering
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Now I understand you. The only thing left I can think off is using a MaterialParameterCollection on every single material. But depending on the size of your project, that’s gonna be fun.

I’m not even sure if you can call it a bug, there is high chances that materials with the UI domain work differently, because they are used in UI which is closer connected to the blueprint system. I’m sorry I can’t help <3