Dynamic lighting cascaded shadows stop working at 250 actors - why?

I’ve got a problem where cascaded shadows just stop casting when I put in the 251st actor. Why is this? The self-shadowing still seems to occur, but no other shadowing.

The shadows are working correctly when there are 250 actors. I have >600 actors to put in. The specific actors doesn’t seem to be a problem, because if I use the first ~200 actors, they come to 30mil tri’s, and adding 1 more actor stops the shadows. When I use the last ~200 actors, they come to 20mil tri’s, and adding 1 more actor stops the shadows. Yes my meshes are large (from CAD models), but the problem doesn’t seem to be tri-count or anything like that, simply it is hitting some limit at 250 actors.

And to make it stranger, if I set the cascaded shadow distance to 84568 or greater, the shadows come back for all parts. I haven’t determined if this number is related to the engine, or the location of my objects? All parts have the same origin, which is the 0,0,0 point in the CAD model. This means I can import each object, and drop it into UE4 at 0,0,0, and everything is in the correct spot. Within the engine world though, this puts the parts out at around -5091000.0, 16390000.0, 68500.0.