I am not sure, if this testing should be the only reason for the sales drop. It seems too simple to me.
There’s a customer forum and I did not find a single message or post or thread, where a customer complains about the new UX design and that it makes him unable to explore and buy items. I am sure, that a long term customer would leave a comment, if the UX design was shredded and makes the envato market unable to use.
Maybe we have a lot of influences to the sales drop I guess. But honestly i cannot identify them all.