Double mesh draw calls since 4.16

I have created a test project with the cool little v4.0.2, added 6k boxes with a basic material then went thru numerous builds to see how the scene performs in there.

It’s actually getting wose in builds around v4.8.2 but then in 4.11 it sped up considerably (the performance build), and it stays kind of the same speed all the way up to 4.15.

In 4.16 (and 4.17 preview 1) the rendering times will increase from 10.8msec to 13msec however! That’s a little over 2msec loss while rendering the same 6k boxes. In the stat scenerendering i did noticed the mesh draw calls got twice that many (for no apparent reason) which means the engine is actually rendering certain things twice. Or the stats gone wrong, but the slow down is still can be noticed!

Why is this? What happened? The test machine is win7 64bit, and a 1070gtx card.

Here are the screenshots from 4.15.0 and 4.17 p1. Same scene, made in v4.0.2 opened in both engine versions for the comparison.

Additionally just tested the stanford dragon (100k tris) placed 625 copies to the scene and in 4.15 i get the expected triangle counts, but in 4.17p1 it is twice that many.

The rendering costs is an additional 11.6msec which is huge, considering i opened the same basic scene with just one directional light present.

Collisions and most rendering features were turned off, including shadows and lightings on the model. I’m using the basic worldgrid material here and the scene were built in 4.15.0.

Comparison images from 4.15 and 4.17p1:

I’m having the same issue and since I’m developing for Gear VR a double increase of draw calls is taking hard on performance. I noticed however that when removing static meshes from the scene where I used modulate blend mode (blob shadows) then I lost the expected amount of draw calls. But with other meshes that has opaque blend mode (almost all other meshes in the game) then I would lose twice as many draw calls which doesnt make sense too me. Did you ever figure this one out and if so how did you do it?
I’m using UE version 4.17.2

Thanks in advance!