Max instance count in PIE?

I have a board game currently being drawn using Hierarchical Instance Static Mesh components. There are a few thousands tiles and all are simply instances of ones mesh.

In the editor viewport this works fine, but when I hit Play in Editor or Play in New Editor window, basically large swaths of tiles just vanish. Not all of them, but large amounts of them. And the ones missing change as you move your view around, with tiles popping in and out. Even worse, in VR it will do this PER eye! So you might see a string of tiles in one eye and not the other.

However if I do a standalone build and play, everything appears to work properly with no missing tiles.

Is there some instance cap in the editor or something?

Hmm it seems to be some weird thing with HISM where if I set the component’s static mesh in the editor, when my construction script runs it does not see that value (Get Static Mesh on it will return null), but yet oddly in the editor viewport it will still draw the instances. Very confusing. Explicitly setting the HISM’s static mesh in the construction script will fix the problem.