Steps to reproduce:

1) Download attached project 'DynamicBatch.zip' and open in Unity
2) Open scene 'CampaignStage_2' and press Play
3) Press U on the keyboard (Prefab will be instantiated in (709f, -1841f, 0f) position)
Note: Prefab will be instantiated in the scene every frame, and 'Dynamic batching: index buffer destination is NULL (first IB byte 0 count 0 first vertex 0 offset 0)' error will be filled in Console
4) Stop Play mode and press Play button again
5) Press Y on the keyboard
Note: Prefab will be instantiated in (709f, 1841f, 0f) position and Console will be empty

Reproduced with:
5.6.0b8, 5.6.0b10

Not reproduced with:
5.5.2p1, 5.6.0b7

Regression since:
5.6.0b8