The stylesheets are still moved to the website footer, to the very end for some reason. By default the plugin enqueues them to the header, so something must be moving them. Because these styles in the footer are rendered just before the page is finished loading, the browser needs a bit of time to process them, thus causing the flicker.
If you want, I can take a look at this directly. Can you please add temporary FTP and back-end access? Thank you!