If you using MASH via an instancer node and of course change the LOD to BoundingBoxes for better viewport performance, the instancer is not show all the objects in Viewport 2.0.
The solutions are:
- Using Viewport 2.0 you have to change the Cycle type to Sequential in the Instancer node.
Of course this is not ideal.
Always learning. 🙂 - Strangely, if you change to Legacy Default Viewport you’ll get all the objects.
Cheers, D
Denes Dankhazi's Blogfolio 
I do have the same issue, and still no fix, I can t use sequential, and I would rather not use legacy viewport. Any fixes since then ?
Unfortunately there is still no fix for this.
Damn! Thanks