If you instantiate prefabs, the RenderBounds (and ChunkWorldRenderBounds) will be added automatically to the prefab. Everything works as usual in this common case. But if you create entities from scratch in the code, you need to manually add RenderBounds yourself now.
This change was made to improve the runtime performance of the bounds system, and to solve fragmentation issues when instantiating entities at runtime. Previously if you instantiated one new entity every frame, you ended up with chunks of 1 entity each. Now the new entities get properly added to the same chunks as existing entities (as their archetype matches).
We are sorry that this breaking change slipped though the change list. Our current entity instantiation test is instantiating prefabs instead of manually crafting entity in code. We will add a new test case that covers this use case too.