Not sure if I posted this before but here are two main problems:
1. if my phoenix sim starts at frame 100 and I start rendering at frame 90 once it reaches 100 and above no phoenix smoke is loaded and rendered.
The only way for octane to render smoke sequence is to start rendering at frame 100 or above. Not sure why octane is not seeing phoenix
2. Another problem when Alpha shadows is on and phoenix grid is in the scene even empty phoenix grid cells increase render time 2-3 times. it is almost like octane sees empty cells as glass making rendering very slow