I can confirm this bug. But in my case there's no failsafe way for me to bring back the preview once it's decided to disappear. Doesn't matter if I close the Octane Viewport, or disable movable proxy or hit update all in Forest Pro. Sometimes it seems to work if I restart Max.
Hi, what Octane and Max version do you use ? We are unable to reproduce that specific issue here (Octane 3.04, Max 2017, FP 5.2.0).
I mean, it's true that viewport would disappear using Interactive Render, but it should come back clicking Display->Update All.
I want to add the Maxscript interface for "Update All" in next FP update, as suggested above.
A complete fix is much more tricky, because each render engine use their own tricks to simulate the interactive rendering (as Octane or Corona). None of them supported by Max, so we must analyze them and write custom hacks.