Hmm, even the scene without problems is corrupted. You can't enter into some of the OBJ nodes or materials without problems or crashes.
To be honest, I've no idea about what could be the problem in this case, and how to fix it. Could be even a bug in Houdini, nothing related to Octane, but it is hard to say. Do you have an early backup of this scene, before starting with these problems? If not, you are going to need to try to build a new scene copy/pasting the assets from the corrupted scene to the new one to see if it helps.
And to be safe, disable the multi-thread scene extraction option available in the Octane ROP node. I'm not sure if the problem could be related to this feature, but this is the only thing that comes to my mind that could be related to this problem if it comes from the Octane plugin.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini