[dirtboy]

Making this mystery even more evolution-defying is the fact that the rock layers below the Cambrian are devoid of invertebrates.

No, they are not.

Edicarian fossils

[Bob434]

From you wikilink

.....Determining where Ediacaran organisms fit in the tree of life has proven challenging; it is not even established that they were animals.....

[lasereye]

That link does not list any pre-Cambrian invertebrates at all.