This seems to be the right place so I'll add my issue which sounds very similar.
In my case I'm rendering through backburner on a 128GB node. During preprocessing RAM consumption shoots up to 125GB (this is already with some elements disabled to fit it in RAM), only to decrease to 52GB - 55GB within minutes once the render process begins.
I can't render the same scene on a 64GB node because of the RAM spike, even though it looks like Corona actually needs way less than that.
I'd happily trade less RAM consumption for longer preprocessing/parsing times if it means I don't have to split a render into 2-4 jobs only to get my elements/masks.
This is with Corona 9hf1 (I know I'm waaay behind) but this issue has been there for quite some time already.