I fingered it out, the vdb was broken.
Artifacts disappeared after I resimulated the smoke.

Hi everyone,
I am using octane2020.1.5.3 for houdini18.351 on linux to render a volcano scene. The video is attached with the post.
output.mp4
I found that the explosion smoke on the right side start flashing and gernerating artifacts on frame 77. It became so obvious around frame 125.
flashing ...