What causes fire to gradually turn off or disappear? I use blender 2.80 (The old smoke simulation). When I bake the last 251 frames of the movie, the fire works well then, it gradually turns off!

Click here to download the blend file.

Here are the steps to reproduce the issue:


Bake.
If you navigate before frame 9039 you will find the fire in the rendered image.
Around frame 9039, the fire gradually disappears or turns off.
At frame 9060, the fire completely disappears in the rendered image.


I need the fire to last until frame 9172 so the fire should be present in this range (8922-9172) without getting weak, disappearing, or turning off.

Q: What causes fire to gradually disappear?
In this case it is camera distance. But, instead usual camera distance, that is located in camera settings, this is volumetric distance, that can be adjusted in render settings