There's issue with new tab switcher. Earlier one use to show page content, but this one show just white nothing. To show content of page in card of tab switcher you have to first view that page fullscreen and then when you open tab switcher it shows content. See:
I noticed the same issue, when you load up some webpages the tabs are white, however when you open all your tabs then they will show a preview picture.
Another issue im having is that there's a delay when opening the tab switcher, sometimes up to a second long. This is on a brand new galaxy s7, closing the tab switcher is instant, but opening it there's a delay.