Blueprint: Random pulse seems to reset after a short while

Hello everyone,

i try to get an Background with static Meshes to pulse an Texture over time.
So far it is working and it is random as i want it to.
But after a while it seems to “reset” and everything is glowing at the same time…

Here is my Glowing part of the Material:

http://puu.sh/BNwbk/bbbe065ddb.jpg

I dont know that i missed here… the Lerp on the right is connected to “Emissive Color”…
I hope you guys could help me with that.

Greetings

Nobody any ideas?
I don´t get it fixed by myself :confused: