A couple months ago I de-optimized my site to huge benefit.
This may the issue. To some degree, to de-optimize is to optimize. And if you de-optimized a perfectly optimized site that was already ranking well, then a ranking drop might be expected. Also, if the site was stale and you made sudden changes to the text, it could cause a ranking drop. I have personally witnessed this. You didn't state specifically if your site was stale, so I am just suggesting it as a possibility.