Performance dropping over time in HelloCube 08

So I am trying out the HelloECS-cubes scenes from 01 to 08 to see what ECS is capable of. I am running it in Unity 2019.2.0a11.

When HelloCube_08_SpawnAndRemove starts with all cubes red I get blazing performance with triple digit fps, however, when the cubes start switching to green it only takes a few minutes until the performance has dropped and I get 30 fps on my GTX1080 i7 32 GB RAM workstation.

The only edit I have done is to toggle off drop shadows on the light as I was intending on testing this on a HoloLens.

Why is this happening?

Related pictograph is the profiler after a few minutes of running (it has settled on 30-31 fps as of now).

[edit] I have now spent a bit more time testing degrees of ECS-involvement for this, and when doing just Job System manipulation of GameObjects I don't seem to get a permanent downgrade in performance over time.